If you cancel your membership prior to your next monthly or annual billing date, you won't be charged for the following month or year. You'll be able to continue to play Vault games, use your discount and jump into any available Play First Trials until your membership expires.
As a member of Origin Access, you'll score an automatic 10% discount on purchases from Origin.com, including new releases and pre-orders. Ditto for expansions, game packs, points, you name it. Please note: to receive the discount, the purchase must be made via Origin.