The gift of tongues is controversial and debated amongst different religions. As I am, non-denominational, I will base my views on the Word of God a.k.a the Bible.
Speaking in tongues is having the Holy Spirit speak from within you in a language most don't understand. Many churches believe that only those who has been given the gift of tongues can speak it, mostly because of the scriptures, 1 Corinthians 12:28-30,"And in the church God has appointed first of all apostles, second prophets, third teachers, then workers of miracles, also those having gifts of healing, those able to help others, those with gifts of administration, and those speaking in different kinds of tongues. God has appointed first of all apostles, second prophets, third teachers, then workers of miracles, also those having gifts of healing, those able to help others, those with gifts of administration, and those speaking in different kinds of tongues. Are all apostles? Are all prophets? Are all teachers? Do all work miracles? Do all have gifts of healing? Do all speak in tongues? Do all interpret? But eagerly desire the greater gifts."
But is says in 1 Corinthians 12:27-31 " And now I will show you the most excellent way.Whoever believes and is baptized will be saved, but whoever does not believe will be condemned. And these signs will accompany those who believe: In my name they will drive out demons; they will speak in new tongues" Which means that anyone who is saved and believe in Christ will have the ability to speak in tongues.
It also says in Acts 2:4 "All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them."
So what is exactly the gift? I believe that the Holy Spirit can choose a believer to speak in tongues and intercede for them when they believe and become close to God but those who have the gift can speak it and teach with it at anytime as Paul spoke about in 1 Corinthians 14. The gift of interpretation,however, is different and given to someone who hears tongues spoken and hears the message in their spirit.