The Bible says the disciples spoke with other tongues 'as the Spirit gave the utterance' (Acts 2:4). When a person is filled with the Holy Spirit, the person speaks with his own voice but the Spirit gives the words in a language the person doesn't know. Sometimes the person may be already speaking in their own language when the Spirit begins to provide the new language. Usually people are praying or praising God out loud when the Spirit falls upon them, but not always.
If you have never had this experience, pray that Jesus will fill you with His Spirit. But don't forget that you must also be baptized by full immersion in the name of Jesus Christ (not in the titles Father, Son, and Holy Spirit). Read Acts 2:28. Also read our article called 'What is the Gospel of Jesus Christ' on the Doctrine shelf of the Apostolic Free Library.