As for tongues, most people don't get this except Pentecostals I suppose, but tongues has THREE functions.
1. It's the only evidence of receiving the Holy Spirit as SCRIPTURE shows. See Acts 2:1-4, 10:44-48, 19:2-6. That's NOT the gift of tongues by the way. That's the sign Jesus talked about in Mark 16:17. YOU don't speak in tongues to get the Holy Ghost. Instead, the Holy Ghost fills you and RIGHT THEN does the Spirit give you utterance to speak with other tongues. That does not teach you need to speak with tongues (the sign) to go to heaven, but it advocates you need the Holy Ghost baptism in order to go to heaven. Tongues is just the only evidence. Some might disagree, but if the Bible says it is so then it is so. I'm no one to oppose how God set the pattern!
2. After receiving the gift of the Holy Ghost, the gift of tongues is a gift you may or may not receive. It's not necessary to receive to go to heaven of course. 1 Cor. 12:30 asks, "Do all speak with tongues." Of course not, seeing this refers to the GIFT of tongues and the not the initial evidence of receiving the Holy Spirit. Tongues as mentioned in 1 Cor. 12:30 is listed amongst other spiritual gifts and 12:31 tells us to covet the best gifts, therefore validating my explanation that it is the GIFT of tongues being refered to here.
3. Last, but not least, is the prayer tongue. The Holy Spirit makes intercession to help you pray for thing you know not to pray for. That's powerful stuff. I've experienced that many-a-time and it really draws you closer to God. For those who disagree, PLEASE give it a try. It really IS for you!
1 Corinthians 14:14-15 says, "For if I pray in an [unknown] tongue, my spirit prayeth, but my understanding is unfruitful. What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also."
This is what Paul was referring to in Romans:
Romans 8:25-28, "But if we hope for that we see not, [then] do we with patience wait for [it]. Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with GROANINGS which cannot be uttered. And he that searcheth the hearts knoweth what [is] the mind of the Spirit, because he maketh intercession for the saints according to [the will of] God. And we know that all things work together for good to them that love God, to them who are the called according to [his] purpose."
Groanings: "sigh, groan, murmer, pray inaudibly"
Back to above verses: 14:16-18, "Else when thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say Amen at thy giving of thanks, seeing he understandeth not what thou sayest? For thou verily givest thanks well, but the other is not edified. I thank my God, I speak with tongues more than ye all:"
Notice the tongue is for giving thanks! (praising God, etc.)
Whether it is public or private, it is to to be done in order.