Learn to use the forum search function, upper right between f.a.q. and home. You will find many informative posts. This question has been asked 100's of times.

Also find a post by ursula and look at the links in the signature line.

I quick answer to your question. The icons designate the file type.

avi and mpg/mpeg are normally of decent quality. A movie is appx. 700MB give or take, and may come in 2 0r 3 parts. Any thing less is usually a trailer or clip.

The rest you can use the forum search to find.