for downloading cc from other sites you need a few things in place before you start
make sure you have your mods folder and packages folder ready
for your mods folder go to documents-electronic arts - the sims 3 right click anywhere here and from the drop down click new, call this folder Mods, open your Mods folder and again right click choose new and call this packages. This is where you are going to put all your package cc files. now you need to get the updated rescource.cfg file this goes into your Mods folder but Not your packages folder I get mine from here
now we need to download a file to open zip/rar files i use this one here
next you need to get these tools delphys dashboard from here
this one checks your packages after you have put them in your packages folder to make sure there are no corrupted/conflicted/duplicated/empty or sims 2 files
delphy's custard from here
this one checks your sims 3 packs for any corrupted files now use this one before you install your sims 3 packs into your game.
both of these tools have directions for use but if you have any problems dont hesitate to ask.
I keep all of these tools in one place so I can easily find them (desktop)
ok now we can download
once you have found your item of cc, download as you would normally do,
click on your little downloads box and right click on your item, then click open containing folder
then right click your item again and use the extract here
once you have done this you will see if its a package or sims3 pack file, for package drag and drop this into your packages folder you made earlier,
now open your delphys dashboard and check to make sure everything is safe
if its a sims 3 pack then open your custard tool and and check this file with that if everything is ok and there are no corrupted files then you can install this safely, this will go to your launcher to install.
its important to make sure all your windows updates are done and everything else is updated too other wise your cc might not show up in game.
another thing to remember is when you are updating your sims game remove your mods folder to your desktop before hand as the update sometimes wipes your cc, you can always put it back when the update is done.
i hope this helps and if i have forgotten anything i am sure someone will jump in and let us know, i hope they do as many heads are better than one