I may be an idiot, but I'm not sure how to
Get 7zip, it's free, and I've only had a problem with it once in a blue moon.
If you don't understand how to unzip a compressed folder, I'm surprised you're even on this site because most if not everything from this site will be in compressed format.
Now, if you already have a rar reader, all you need to do is right click, open with the rar reading software, then click and drag the contents to another folder outside of the rar reader window. This should automatically decompress the contents. Alternatively, you can right click and (using 7zip) you can click extract files, which will allow you to enter a folder path for the contents to go. (Personally I find it easier to just click and drag.)
A good practice when trying a new game, keep the rar file until the game works 100%. If it doesn't work correctly by freak chance it could very well be the decompression. Delete the game files, and start over with the rar. If the decompression fails twice and the game still doesn't work, it's probably not the rar software.