The Biblical gift of tongues is where you are preaching the Gospel in what seems to you to be your own language, but the Holy Spirit is translating it perfectly into one or more languages that the hearers know (Acts 2:4-12).
The problem with this view ^ of tongues is if that was what the Apostles did on the day of Pentecost, then Peter would not have had to stand up and give his sermon that follows immediately afterward. If the tongues they spoke were in fact the Apostles preaching the gospel, then that sermon would have not needed be spoken. Another post says that tongues today are jibberish languages because other false religions practice it too. But if there is a false something, then there must be a true something. You can't have one extreme without the other. Hot/cold, Rough/smooth, truth/lie, tall/short.... Usually those who hold this view are either ignorant of what scriptures teach on the subject or they are fearful of those things that are different than what they believe. I grew up in a Baptist church that still to this day teaches those who claim to be Spirit-filled may in fact be demon possessed because the Holy Spirit no longer fills individuals as He did in the book of Acts. No where in the Bible, not one verse says this though...
Speaking in tongues is just an outward manifestation of a miracle that has occured within each of us. But before you can understand tongues you need to understand different ministries of the Holy Spirit, look at this...
In John 20:21, Jesus says receive the Holy Spirit to the disciples and breathes on them. Look back in Genesis when God created man, He breathed life into man and man became a living creature. This is symbolism that Jesus breathes new life into the believer and they are thus "born again" (John 3:3; 2 Cor 5:17) There is no mention in this passage of speaking in tongues or fire from Heaven or Wind from Heaven as there is in Acts 2:1-4, so the accounts must be different. Why would John, a man present on that day of Pentecost, the man closest to Jesus, have omitted such a powerful testimony from his record there in John 20 if that was what he was talking about. John's account is of the church entering the new covenant that Jesus enacted with His blood (Matthew 26:28; Hebrews 9:11-28) A different thing from the Pentecost experience with the Holy Spirit that does not result in tongues but instead eternal life.
In Acts 2, we see that the Holy Spirit falls upon the early church and all present there are filled. During his great Pentecost sermon, Peter says that the things the crowd saw and heard was in fulfillment of Joel's prophecy that in the LAST DAYS God would pour out His Spirit upon all flesh. Peter makes that connection and says it was fulfilled by Jesus receiving the Holy Spirit from the Father then POURING Him out upon those who believe resulting in those outward manifestations (see and hear, 2:33) In Romans 5:5, we see Paul saying that when God pours out the Holy Spirit on a person, it's into their heart. Once again when God pours out the Holy Spirit, it is to fill, not to indwell. Jesus told the disciples repeated to wait in Jerusalem until they received the Promise of the Father (Luke 24:49; Acts 1:4) which He explained as being the Baptism in the Holy Spirit (Acts 1:5) That is one of the reasons Jesus came to Earth and died for us was so that we could have this dynamic new relationship with God. God doesn't just want us to have a love letter from Him (as some call the Bible and rightfully so because it is) He wants us all to experience Him and know Him personally and intimately. The Baptism in the Holy Spirit is the first step in that walk. God promises He'll pour out His Spirit upon us, we have to receive it in faith, just as we received salvation. Just as salvation is of God's grace, so too is the Baptism in the Holy Spirit. Peter at the end of his Pentecost sermon said that we must repent and be baptized (in water) to receive the gift of the Holy Spirit (Acts 2:38) which in the very next phrase (2:39) Peters says in the Promise of the Father. Once again Jesus Himself said the Promise of the Father is the Baptism in the Holy Spirit (Acts 1:4-5) Notice something else about what Peter says in Acts 2:39. That the Promise is for all who the Lord calls. If the Lord has called you for salvation then you can have the Promise of the Father, the Baptism in the Holy Spirit as well, receive it in faith (John 7:37-39; Acts 2:38-39)
So back to the point at hand, we've established that when God breathes the Holy Spirit on us, it's at conversion and gives us new life (Eph 1:13-14; John 20:21; 2 Cor 5:17) and when He pours out the Holy Spirit on us it's to fulfill His promise in Joel 2:28-32 (Acts 1:4-5; 2:33; Romans 5:5; Titus 3:6)
When God pours out the Holy Spirit into your heart to fulfill His promise He does so into your heart (Romans 5:5) Jesus said in Matthew 12:34 that the mouth speaks from what comes out of the heart. In John 7:38 Jesus says that those who believe will have streams of living water flowing from within them. If you read the very next verse, John explains this to be Baptism of the Holy Spirit because the Spirit had not yet been given because Jesus was not yet glorified. Jesus was not glorified until He ascended in Acts 1 and as we have seen there are two instances of Jesus with the Holy Spirit and giving the Holy Spirit to believers, one in John 20 and the other in Acts 2. In John 20, He breathes the Holy Spirit while physically present with the believers on Earth, whereas in Acts 2 Jesus pours out the Holy Spirit while seated in Heaven. So to meet the criteria of John 7:37-39, we must accept that this is talking about the Promise of the Father, the Baptism in the Holy Spirit. So God pours out the Spirit into your heart (Romans 5:5) and the Spirit overflows from your heart (John 7:38) and you speak as a result (Matthew 12:34).
So very literally, speaking in tongues is the Holy Spirit overflowing from your heart through your mouth. It is the most beautiful thing. That is also why many, including myself, believe that when you are Baptized in the Holy Spirit you will speak in tongues, but as with everything else in our walk with God it must be accompanied with faith (Hebrews 11:6)
Tongues seem like nonsensical jibberish because we don't understand them, that doesn't mean they are not real. Having that approach is the same as the Jews in Jesus day that continued to demand He produce a sign for them to believe He was real, one that they could physically see Him do, because they could not believe what someone else said about His works, they lacked faith. In 1 Corinthians 14, one of the most detailed passages on the subject, Paul says in verse 2 that no one understands a person speaking in tongues, they are speaking to God in mysteries. When you hear a person speaking Chinese or Greek or whatever language you don't understand, does that mean they are not speaking a real language just because you don't understand it? No, that just means you don't know what they are saying. Sometimes the Holy Spirit gives an interpretation, if He does then that is a gift of tongues as laid out in 1 Corinthians 12:10, but every Spirit-filled believer will speak in new languages (Mark 16:17-18; Rom 5:5 -> John 7:38 -> Matthew 12:34) Some say that if God wants me to speak in tongues then why doesn't He just make me do it? Well God will never force Himself upon you or any of us. He gave us a free will and we are free to choose what to do with ourselves. He will never force Himself upon anyone, if we want more of Him, we must ask, seek and knock to receive (Matthew 7:7-11; Luke 11:9-13) Even the first time tongues are spoken in the NT (Acts 2:4) notice God says that THEY SPOKE as the SPIRIT GUIDED THEM.... So they opened their mouths to speak and the Holy Spirit gave them the words...
When I spoke in tongues for the first time it was the same way... I was praying in my room and as I drew closer to God in prayer I just began speaking new language I'd never heard before. Satan will try to convince you that it is not real, that you are making it up, that you are doing it all yourself. Don't let him fool you. He tries to keep us from praying in the Spirit (Speaking in tongues) because it's such a powerful weapon for believers to have. Satan can no more understand what you pray in the Spirit than what you can, he is not omniscient as God is. So if you can't understand what's spoken, neither can he. The Spirit is speaking directly to God from your heart, bypassing your mind, your understanding, your will (Romans 8:26-27; 1 Corinthians 14:2, 14) Don't be discouraged because you can't understand.... Have faith that you are speaking directly to God with your words and remind the devil he is a liar and father of lies (John 8:44) God is the Truth and has promised that when you ask for something good, you'll never receive anything bad! (Matthew 7:7-11; Luke 11:9-13) Be strong have faith!
Lastly, all this and all the Spiritual Gifts are great and wonderful to possess but without love, genuine love for God and others, then you can have the highest anointing to ever exist and yet it would do you no good in the sight of the Lord (1 Corinthians 12:31-14:1) So once you receive, and you will, do not look at that as you have arrived and need to further to love or obey, spiritual gifts are a grace of God (the word gift is itself charisma which means a specific act of grace) God gives them to us to use for others (1 Peter 4:10) not to keep to ourselves or puff ourselves up with pride and brag that we can move mountains with our faith or speak the languages of angels.
I hope this was helpful to you

PM me if you have any questions.