Re: How to use pre made sims in sims 4

Sims can be brought in from the Gallery either Create A Sim (CAS) or Live Mode. In CAS, the Gallery button is in the upper right, next to the Save Household button (it can also be opened by hitting F4). Find user-created households under the Community tab. Clicking the Save icon will bring a household into your Library in the Gallery, and hitting the Wrench icon will bring that household into CAS so you can edit them.

Source: http://help.ea.com/en/article/the-sims-4-gallery/

This might help you as well:
http://getsimplyruthless.blogspot.nl/2014/09/tutorial-using-sims-4-gallery.html