Hey! First of all, do you use a Mac? The Clean Installer doesn’t work on Macs (unless you have a Windows partition, I would think?). :
If not, after you install the program, double-click on any Sims2Pack file you have downloaded (in this case, I opened the sushi restaurant), and it should bring up a window like this:

This is a list of all the CC that comes packaged with the lot. You can look through exactly what’s packaged to decide what you would like to install into your own game, and you can uncheck anything you already have (to avoid duplicates) or anything you don’t want installed. 🙂
The first item listed (Izumi Sushi) is the lot itself – you can check under the “Type” column. 🙂 If you ever download something because you want CC it has, but not the lot/Sim itself, you can uncheck this and the Clean Installer will just install the CC you leave checked. 🙂
When you’re satisfied with the content you have checked or unchecked, just click install!
Just a note: lots don’t package any Maxis recolors, unfortunately, and they will not automatically package the master meshes for any slaved meshes you use, which is why I try to include a folder (in addition to the Sims2Pack) with the other required meshes/recolors.
I hope this helps! Feel free to message or chat if you have other questions. 😀

