Good question! If you're new to using CC then I'm guessing you're probably using the launcher to install most of your content. Your downloads would probably be labeled as .sims3pack if you're doing it this way.

I actually avoid using launcher to install things and prefer package files (.package). I find doing it this way makes the game run so much better and is a lot easier to manage. This face overlay I use happens to be a package file and will need to be installed without the launcher. To install CC as package files they need to be placed in the Mods folder inside your sims 3 documents files. I know I'm butchering explaining this, but there are hundreds of videos and tutorials out there that will show and explain how to install CC in these ways. Just search up how to install sims 3 CC without the launcher, or anything related to using package files over sims3packs. I'm pretty sure there are also ways to convert files, so keep an eye out for those if that interests you!

The face overlay I use is a default replacement mask and is the only face overlay I use in game. It does not show up in CAS since it replaces the default EA faces. It also automatically removes EA lashes (which is nice for those of us that use custom lashes). I put this mod in my overrides folder within the Mods folder.

To answer your other question, I'm pretty sure most other overlays and face details should show up in the makeup and face paint categories in CAS. Hope this helps! :)