Question about last step on "how to install sims correctly"

little confused on the very last step, I understand to replace the base game files with crack, but I have also installed some expansions so what do I do with the other files located in the ultimate fix? Also where  do I launch the game from?

Welcome to our Forum! Are you talking about the step below?

5. Open the "# Crack" folder in the Ultimate Fix and drag & drop the .exe and .dll file in there to exactly: C:\Program Files (x86)\Electronic Arts\The Sims 3\Game\Bin   and choose "Copy and Replace" on the pop-up that appears, telling you the files already exist in that folder.
(If you downloaded and installed your base game via Origin, the crack goes into this folder instead: C:\Program Files (x86)\Origin Games\The Sims 3\Game\Bin )
Ultimate Fix video tutorial (old, out-dated): https://www.youtube.com/watch?v=TrRrF5ysPa8

As you can read above, you just need to replace the base game files, but you should do it again after the last expansion installation.

Please let's know if everything is working properly.

Happy simming!!