If you receive a .rar file as an email attachment, simply double-click to open it.
If you have saved a .rar file in the Finder, double-click it to open. After opening it, you can view some or all of the contents by highlighting the files and pressing Command+Y.
To unzip the contents, follow these steps:
With WinZip for Mac 2.0 or later, you can right-click (or press CTRL and click) your saved RAR files and use the Context Menu to unzip them. Click on Services at the bottom of the Context menu, then choose Unzip.