In The Sims 4, there is a folder called Tray for lots and Sims. It is located in:

Windows XP: Documents and Settings\(Your User Account)\My Documents\Electronic Arts\The Sims 4\Tray

Windows Vista, Windows 7/8, Mac: Users\(Your User Account)\Documents\Electronic Arts\The Sims 4\Tray

Lots and Sims use several different types of files. Both use a type known as .trayitem . Lots also use .blueprint and .bpi files, while Sims use .hhi, .sgi and .householdbinary files. These files can be installed by extracting them from the archive file they are in, and placing them in the Tray folder; there is no need to do anything else to them.

You must unzip the file and place only the tray items in your tray, not the zip file.

Once you have placed them there, you should be able to find the Sims or Lots in ''My Library'' in the game once you launch it.