@Ilikefruitcake12 To answer the question you don't care about as much first, Steam doesn't accept product keys from disc or Origin purchases of Sims 3 content. It probably has something to do with the terms of the deal with EA to sell the game, but the point is there's no way to get your other keys into Steam.
You get 1,000 SimPoints for registering each of the Sims 3 base game and World Adventures, but not usually any other packs, unless you get lucky and happen to find a limited edition pack somewhere. (There's also an occasional glitch in the store where you can keep clicking the Redeem Points button over and over, and get 1,000 more points each time, but that's not intended behavior.) You can register the keys either in Origin or on the Sims 3 Store site, but if you do the latter, make sure you're using the same account, because points don't transfer from one account to another. You can register keys from Steam or from discs; the Origin purchases will already be added to your account.
Installing store content works the same in Origin, Steam, and disc installs: you download your items from the store site and install them through the launcher. The one catch is that if your Steam base game code isn't registered in Origin and you're playing through Steam, you may not be able to use the store content: it's encrypted and checks the key of the installed game against the key of the account that owns the content. The solution is just to register your Steam key as well.
