After you have downloaded AND installed the WinRAR program, shutdown your computer...
This is always a good habit to follow after installing any new programs...

After you start your computer again you simply double-click on the .rar file that you have.

There are a few details involved in the first setting up of WinRAR, such as where the OPENED or 'unzipped' files will be stored, but I'm sure you'll work it out.

In WinRAR, after you have clicked on the file you want to open, you will see a screen with all kinds of crazy buttons to press !!!

Just click on EXTRACT TO and choose a suitable folder... DO NOT 'extract' files to your main C: folder... It's best, really, for when you are first using the WinRAR program, to first create a folder with a name that refers to what you are unzipping... 'Extract To' that new folder you have made.

There are also some nice Help files that are included with WinRAR.
This may all seem a pain to you right now, but it is very important, for general use of any computer, to know how to use programs such as WinRAR and WinZIP...

Hope it helps !