I think you just want to watch the files on your computer right? If so, try this thread:

Codec/Player info

VLC player (halfway down first post) is usually recommended.

If you want to convert your movies, that's a different topic.

RAR files are compressed files. You need a program to decompress, or open, them. 7-zip is free and will open RAR files. Link here: www.7-zip.org

Good Luck