This free audio Bible study asks and answers 19 questions about tongue speaking. There is also a PDF file which contains this information in the form of text.
Acts 2:1-3: And when the day of Pentecost was now come, they were all together in one place. 2 And suddenly there came from heaven a sound as of the rushing of a mighty wind, and it filled all the house where they were sitting. 3 And there appeared unto them tongues parting asunder, like as of fire; and it sat upon each one of them.