To fully understand tongues, one is going to have to read about 4 chapters in 1Corinthians. And they are 12 through 15. Speaking in unknown tongues is not impossible, but there are strict guidelines that must be followed. Probably the best example of that is
1Cor 14:18-19
18 I thank my God, I speak with tongues more than ye all:
19 Yet in the church I had rather speak five words with my understanding, that by my voice I might teach others also, than ten thousand words in an unknown tongue.
Paul admits to speaking in tongues here in verse 18. As a matter of fact he's saying that he speaks in tongues more than anybody around him. But he gives different advice when it comes to being in the Church.
Verse 2 of the same chapter proves that it is not a known language:
2 For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.
This is controversial because so many people abuse the gift. To me speaking in tongues is more of a private thing than a public thing. But definitely, read those 4 chapters if you want to know more.