Most of the creations come from the sims 3 website so you have to be a member of the sims 3 website to download them but some creations are created by me and others so you need to download with a MediaFire link. It's really easy!
First click on "download". There are 2 choices:
1) You see a page with the creation, you just have to click on "ajouter au jeu" and the creation will be in your sims 3 launcher. You just have to install the items with your launcher OR
2) you see a page with a mediafire link, click on "download" after that click on "save as" and put the creation in "downloads". To find "downloads": my documents -> electronics arts -> the sims 3 -> downloads. After that open your sims 3 launcher and look in downloads: there is the creation! You just need to install it!