You need to create a Mods folder in your \Documents\Electronic Arts\The Sims 3 and then create a package folder in the mods folder. Then it would look something like:
\Documents\Electronic Arts\The Sims 3\Mods\Packages
Here's a thread that might help:
Creating a Mods Folder/Installing Mods Step by Step Guide
http://www.carls-sims-4-guide.com/forum/index.php/topic,9187.0.html