1 Corinthians 14

Even things without life, whether flute or harp, when they make a sound, unless they make a distinction in the sounds, how will it be known what is piped or played? v.7

Read chapter 14
If someone speaks in a tongue, what is it you first think of?  Babble right? Unintelable sounds?  Many Christians and churches are said to "speak in tongues" like this, yet scripture does not describe speaking in tongues this way at all.  Now I can't explain why it is that this happens then today, other than deceit by themselves or Satan.  One of my friends grew up in a charasmatic church that spoke in tongues and he says he remembers the pastor teaching him how to do it by repeating the same word over and over again till it becomes something more.  Ridiculous right?!  Paul even tells Timothy to avoid idol babbling falsely called knowledge in 1 Timothy 6:20.
Well what is a tongue then?  A tongue is a known language.  It is the same Greek word that has been translated into two English words: tongue and language.  So the gift of language or tongue (which ever word you chose to use) is someone being able to speak another language like Spanish, Mandarin, Hebrew, etc without having studied; he's fully fluent the first time he opens his mouth.  We see this for example in Acts 2:1-12 at Pentecost when men had traveled from all nations heard the apostles speaking in tongues saying that they each could hear them in their own language what the Holy Spirit was saying through them.
I am bilingual English & Spanish but I had to study my butt off to learn a second language.  Oh I wish it was as easy as just being able to speak without having studied which is why that is a spiritual gift, a gift from God.
So how do you now understand the phrase speaking in tongues?  There is a deep study and article by Bible Teach Otis Sellers to check out Biblical Gift of Tongues