Installing content in The Sims 3
Patch your game
The downloaded files on TSR can be sims3packs, package files or zip files. In case you get a ZIP after download, use the built-in ZIP handling in the operating system to extract the Sims3Packs or packages from the archive(s). If you need more information on this, check this help page by Microsoft.
Double-click the Sims3Pack you have downloaded and it will install into the game.
If you have downloaded a lot of Sims3Packs, place them into: Documents/Electronic Arts/The Sims 3/Downloads. If you downloaded ZIPs, you first need to extract the Sims3Packs from them, then place it in the Downloads folder.
Start the Game Launcher and go to the Downloads tab. Select the items you want to have in your game and click Install. Remember to uninstall an item first before you reinstall it.
In the game you recognize the custom content by the shopping bag.
Place the package files into Documents/Electronic Arts/The Sims 3/Mods/Packages. If you don't have that folder yet, follow the instructions below.
Creating a Mods folder
In the Documents/Electronic Arts/The Sims 3 folder, create a new folder and name it Mods. In this Mods folder create again a new folder and name it Packages.
Download the resource.cfg file and place it in the Mods folder (not in the Packages folder):
Note: If you receive a security warning such as this, click KEEP. This cfg (configuration) file is a perfectly safe and can only be used by The Sims 4, but as cfg files are used for all sorts of apps, operating systems do treat them cautiously.
You can now place your downloaded package files in the Documents/Electronic Arts/The Sims 3/Mods/Packages folder.