It's easy but takes some time,all you have to do is complete your goals/wishes!!!! I did about 3 and then a note came up and said that you unlocked new furniture. It may take more time for others!!!!...
Once you download an object (hair clothing furniture ext.) you have to go to the sims 3 launcher (What pops up to play the game) and click on downloaded content. The item you downloaded will be...