"When the day of Pentecost came, they were all together in one place.  Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting.  They saw what seemed to be tongues of fire that separated and came to rest on each of them.  All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them."  Acts 2:1-4

'Other tongues' are supernatural utterances given by the Holy Spirit.  Languages never learned by the speaker, not understood by the mind of the speaker, and nearly always not understood by the hearers.

Paul devotes almost a whole chapter to speaking with tongues in I Corinthians 14.
There are not too many subjects on which a whole chapter has been written.  Prayer is of the utmost importance.

Water baptism is important.  It is a very important subject, but do you know anywhere in the Bible where a whole chapter is devoted to the subject?  No, there isn't one.  The new birth or being born again is an important subject.  Do you know anywhere in the Bible where there is a whole chapter on the subject?  No, you don't.  But there is an entire chapter devoted to speaking in tongues.  That doesn't mean that it's more important than anything else, it just means that it's just as important because God doesn't put unnecessary things in His Word.  This teaching on tongues is important.

Look at I Corinthians 14:2,  "For anyone who speaks in a tongue does not speak to men but to God."  He is not talking at this time about ministering tongues in public assembly.  He is taking about the individual Spirit-filled believer taking in tongues in his own private prayer life.  It is also right to pray in tongues at the altar because you go there to talk to God.  When someone ministers tongues in a public assembly, God is speaking to us and therefore interpretation is necessary.

Weymouth's translation says, "in the Spirit he speaks divine secrets."   God has devised a way whereby we may speak supernaturally to Him.  We talk secrets with God.

Then, in the 4th verse of chapter 14 he says, "He who speaks in a tongue edifies himself."  That means he builds himself up spiritually.  Jude says in the 20th verse, "But you, dear friends, build yourselves up in your most holy faith and pray in the Holy Spirit." It does not say that praying in the Holy Spirit will give you faith, but it does build you up in your most holy faith.  It is a means of spiritual edification.

Paul says in I Corinthians 14:14, "For if I pray in a tongue, my spirit prays, but my mind is unfruitful."  Whenever you pray in tongues you will never leave that place of prayer with the feeling that you didn't say what you wanted to say because your spirit enable by the Holy Spirit that dwells in you always knows what to say.  Romans 8:26 says, "In the same way, the Spirit helps us in our weakness.  We do not know what we ought to pray for but the Spirit Himself intercedes for us with groans that words cannot express."  And the Holy Spirit always prays according to God's will.  Verse 27 says, "And He who searches our hearts knows the mind of the Spirit, because the Spirit intercedes for the saints in accordance with God's will."    

Heavenly Father, I am Your child for I believe in my heart that Jesus has been raised from the dead and I have confessed Him as my Lord.  Jesus said, "How much more shall your heavenly Father give the Holy Spirit to those who ask Him."  I ask You now in the name of Jesus to fill me with the Holy Spirit.  I step into the fullness and power that I desire in the name of Jesus.  I confess that I am a Spirit-filled Christian.  As I yield my vocal chords, I expect to speak in tongues for the Spirit gives me utterance in the name of Jesus, Amen.