Launch your game and then exit out of it (it seems random but this step is important to create the mods folder).
Go to your “My Documents” or “User/Documents” folder on your computer and then find the “Electronic Arts” folder.
Open the “Electronic Arts” folder. It should have another folder in it called “The Sims 4”. Open it. Inside, you should see yet another folder called “Mods”. Open the Mods folder (it should have a resource.cfg file in it).
Now, every time you want to add a new mod, just drag it into this “Mods” folder.
When you open The Sims, you should get a popup with a list of all the mods you have installed.
If you have downloaded any script mods, then make sure to enable them in your in-game settings.