I moved this to it's own thread in the help section because it's not really a site issue per se, inasmuch as it's a problem you need help with.
Yes, you need to unrar/unzip the file. Winrar is
here. Click on Downloads (on the left side of the page) and you'll be taken to the downloads page. If you want the latest beta version (3.80-still in testing) it's up at the top. If you want 3.71, just scroll down. It says 'trial' version, which means after thirty days you'll get a pop up window you'll have to click past.
7-zip is another program people use.
If you have all the meshes (double and triple check that), it could be the cc uses an EP or SP you don't have.
Are you unzipping to My Documents/EA Games/The Sims 2/Downloads? And is your Downloads file spelled exactly as I've spelled it here (capital D and an s at the end). If not it will cause some cc to not show up.
You could also need the latest
CEP for some of it to show up.