simplyUnRAR is one of the simplest applications you will find to work with compressed files and decompress them.
You don't have to run it, you only have to place the icon in the dock and drag and drop the file you want to decompress.
It works with RAR files. Click the RARf file you want to extract files from, drag it to the icon of the application and SimplyUnRAR will do the rest.
It's extremely easy. If you have to deal with RAR files, SimplyUnRAR will help you a lot.