You can easily add your downloaded sim files to your game. All you have to do is move the files to the tray folder. If cc is used in the sim you downloaded, you must download cc leride and put it in your mods folder.
The houses and lots are installed into the Tray folder inside the sims 4 folder.
For most people, it should be in
Documents > Electronic Arts > The Sims 4 > Tray
Open the downloaded file.
Drag all the files inside to the tray folder.
NOTE: If you throw it with folder, the game will not be able to see it Be sure to discard the files inside.
Open your gallery by pressing F4.
Select “My library” from the tabs.
You should now be able to see the sim in my library. If the sim contains cc, make sure the “Include Custom Content” option is selected otherwise you won’t be able to see it.