They spoke in other languages/tongues, not gibberish. The purpose was so that those visiting Jerusalem for the festival of Pentecost and who spoke other languages would be able to understand the good news of Christ.
Free Printable Structural Chapter Reading Chart: The Old Testament. This is a chapter checklist that helps you track your reading progress, while also teaching you the larger outline of the Old Testament. If you're going to use a reading chart, you might as well learn something from it, right? :) Great for kids and adults!