Once you're in game, you'll also need to enable mods in your game settings by going to your Options menu under the Other tab. Your mods folder is located in: Documents/Electronic Arts/The Sims 4/Mods. The game should automatically have created one for you after you start up the game for the first time.
To install Sims 4 mods, you can drag and drop the mod folders you've downloaded into your Sims 4 'Mods' folder. How do you install mods for The Sims 4? Luckily it's pretty simple, especially if you only want to make a couple tweaks.
