The Sims 4 Studio is a tool you will need to start making your own custom content. S4S can be used to make all kinds of cc including but not limited to. Clothing recolors, new object meshes, wallpaper recolors, and animations.
The Sims 4 Studio can be used to just recolor objects, to making a whole new object completely. If you just want to recolor an object all you have to do is export the texture. Then bring it into a photo editor of your choosing and color away. Once you are done Import it back in and voilà! You have your newly recolored object. If you want to make a more complex object then don’t forget the Sims 4 Studios partner in crime Blender! If you want to do anything more than a recolor then you should download Blender 2.79. Blender 2.81 is currently available but does not work with Sims 4 Studio, so be sure to download 2.79.