The first thing you need to understand is that .rar files are not multimedia files, so you usually can't play them right away. A RAR file is an archive, just like .zip or .tar, that can contain one or more compressed files. You can "extract" those files from the .rar archive and play them in your favorite music/video player.
Extracting And Playing RAR Files
The most popular software for extracting RAR files is WinRAR, a shareware application . If you have WinRar installed, you can play .rar files by performing these steps :
Right-click the file in question.
Choose "Extract Here". This will put all the contents of the archive file in the same folder as the .rar file.
Locate the multimedia files created (.avi, .mpg, .mp3 or similar) and double-click to play.
Special Case : Partial Downloads
Sometimes a video file is split among many smaller RAR files. If you have all the parts you can play it as described above, but what if some files are missing or "broken"? You can still play at least part of the video. To preview the video, follow these steps :
Locate the first of the .rar files. Depending on the version of WinRAR used to create them, the first file will either have "part1" in it's name, or it will be the only file with the ".rar" extension (other files will have extensions like ".r01", ".r02" and so on).
Right-click the file and choose "Extract Files...". A dialog box will appear.
Tick the checkbox that says "Keep broken files" (it's in the lower left corner).
Click OK and wait while the files are decompressed. Eventually an error message will come up, click Cancel.
Now you have a video file that you can play in any video player that can handle broken files.