Speaking in tongues is a supernatural way of communicating with God. Speaking in tongues will build you up, allow you to pray for things that you have limited knowledge of, enable you to receive special insight in situations, and give thanks well.
After receiving the infilling of the Holy Spirit and speaking in tongues, a believer should pray in other tongues everyday. In private you can pray in tongues whenever you choose for as long as you want.
Two of the nine gifts of the Spirit are publicly speaking in tongues and publicly speaking the interpretation of tongues in your own language. In your public and private prayer times, you may at times have an interpretation, but this is not necessary.