How to convert an .avi video so it's compatable with iMovie?

Ok, so i took an amateur video on an amateur camera. All I want to do is to be able to put it onto iMovie so i can get the scratchy sounds out. But when I open iMovie and drag the movie in there, iMovie won't take it. So i look at the video and i see that it's .avi . So it's safe to say that iMovie doesn't take .avi videos. Could someone please help me find what video extensions are compatable with iMovie and how i could change my video to that extension? Thank you SOOOOO much!!!