How to install these files?

After downloading the file unzip or unpack(with WinRar/WinZip or 7-zip) them in the sims 3 folder:
C:\Program Files\Electronic Arts\Thee Sims 3\Mods\Packages

Objects often come in sims3packs, install them with the launcher or convert to package with Delphy's multipack extractor

When you want to enable custom content for the sims 3 and make these files actual work ingame then you must go here
and follow the instructions given!!