once you've made all your Keep choice, you want to click the option that says "Export to DAI", then it'll let you save your world-state.
Whenever you fire up your PS4 to play, there should be an option to sign into your Origin/EA account. Once you do that, and then start a new game of DAI, it should then ask if you want to import your Keep settings.
If you've already started a game... you're kind of out of luck, because then it'll just pick the "default" choices for all those past events. (Dalish Female Warden from first game, etc). So you'll need to start a new game to be able to take advantage of Keep.