To unpack a rar files you must have softwares like WinRAR, 7-zip, etc
You can get WinRAR from http://www.rarlab.com/download.htm
1) Right click on any rar file.
2) Then click on 'Extract files...'
3) Type in your destination and hit 'OK' to unpack to that location.
Your files will be Unpacked and ready for use.
Note:1) You can Unpack a password protected rar file, only if the password is known.