Watching 1 ad equals 5 free Simpoints and the number of videos available to you will vary depending on inventory (This can mean The Sims 3 content you own, location or websites you have visited). You can find the feature on the frontpage of the store between branded content and make me an offer.
If you cannot see it, there are two things you can do:
1. Log out and back in, then wait for at least 2 minutes on the store page.
2. Turn off your adblock, the bonus Simpoint features gets seen as an ad (technically it is one) so your adblock program will remove it from view.