Extracting with WinRar (.rar files)
WinRar is the program used to extract .rar files:

WinRar can be downloaded
here for a free trial. However the program seems to work even after the trial has expired.
1. Locate the file you've downloaded on your PC and double-click the .rar icon to start WinRar.
2. Select the
Extract To button to start the extraction. This will open a new window where we choose the location to extract the files to:
Select the location of
My Documents/ EA Games/ The Sims 2/ Downloads by selecting the folders in the window or typing in the location to the Destination Path. This is the default location for all downloads but you might need to check the website you're downloading from incase they have specific instructions, especially if they are hacks.
Once you have selected the right location select
OK. You might want to open your Downloads folder to make sure they've been extracted correctly. Then restart your game and your downloads should appear.