Previously, the Sony Rewards program would only award points for PSN purchases if you paid with a Sony credit card, but now all purchases from the PlayStation Store and the Sony Store, as well as Sony-related purchases from select online retailers, will earn you points.
Step one is to link your PlayStation ID with a Sony Rewards account (or create one), and from there you'll get one point for each dollar you spend in the PS Store. You'll also get a point for each dollar in a Sony Store, and some points for PlayStation-related things you buy online from GameStop, Best Buy, Wal-mart and Target through the Sony Rewards portal. If you have a PlayStation card, you get bonus points when you make those purchases with it.
At its base, this is a sort of 1% cashback kind of deal as 1000 points equals $10 PSN credit, and the points requirements for other rewards like PS+ memberships and games generally match up that way with their listed prices.
This program is US only, and you can sign up here. You get 100 points if you do that by November 12.