It's already been explained above, but it could perhaps be helpful to think of it in these terms:
According to God's Word, we are a royal priesthood. (1 Peter 2:9)
This means that we all have access to God as His dear children. A clear practical example of this is the Lord's Prayer, where our Lord teaches us how to pray to God, and in that, what He desires to give us and His promise of receiving our prayers. A different example could be that He has graciously given us all the gift of the Holy Spirit! So in this sense, we are all priests.
However, this does not mean that everyone is called to publically teach God's Word and administer His gifts of Baptism and the Eucharist. This is (ordinarily) given to those who are called by God through His Church to occupy the pastoral office. (cf. James 3:1, 1 Corinthians 12:29, 1 Timothy 3:1-7)
So, we have a universal call where we can and should profess our joy and hope in Jesus in our various vocations or stations of life. That is, we are all free to preach Christ and everything He has done for us to our friends and neighbours. Everyone is free to call people to repentance and faith and share the good news of God's forgiveness of sins and life in Jesus. But God has also instituted a pastoral office, which is for the public administration of His Word and Sacraments, where the fullness of God's Word is preached and His gifts of Baptism and His body and blood are given for our comfort.
In short, the Bible gives us the following:
- A universal priesthood (1 Peter 2:9)
- A teacher office (1 Timothy 3:1-7)
- A helper office (1 Timothy 3:8-13. You can also read about the institution of this office in Acts 6)
The word "preacher" can be assigned to any of these, though, historically, it mostly refers to the teacher office, which is to say Teacher/Priest/Pastor/Bishop/Overseer/Elder/Presbyter.
We can take joy in that our Lord has given us all equal access to Himself. He has graciously given us His name that we may call upon Him in every trouble, pray, praise, and give thanks. And we can share Christ wherever we are! We don't have to be a pastor to share the Gospel. But if we do aspire to the office of overseer, we are given these words: he desires a noble task. Meaning, it's good and commendable. So my practical advice is this: If you want to preach God's Word to your friends and neighbours, God be praised! However, if you want to serve a congregation as a servant of the Word, it's good and right to seek ordination, which means allowing the Church to help you, equip you for the office, and lay their hands on you.
God bless!