.rar is a basically used for to compress files and make them smaller. .Rar files can be changing into equally sized parts for archiving and they can also be password protected. To open a .rar on your Mac, you usually want special software.

Try this:

• Use a decompression tool kike UnrarX to open .rar files on a MAC. UnrarX is available for Mac OS X 10.0 and higher.
• Download software like RAR Expander, which supports Apple scripts.
• Open .rar files on your Mac by dragging the files and after that sinking them onto the icon for your expander software. The software will then decompress and open the files so you can use them.