First, I very strongly recommend that you start at the beginning and take the time to work through these basic materials to learn After Effects:
Your questions show a lack of basic terminology, so it's going to be very hard for us to help you until you learn at least enough so that we're using the same language.
Regarding QuickTime: You need to install QuickTime. You can get it from the Apple website.
Regarding large output files, heed Rick's advice and use the FAQ list for this forum, specifically this item:
Finally, it sounds like you've turned on auto-keyframing. If so, turn it off.