From what I’ve read, Genie will do a couple things:
1. Give you proposed itineraries based on preferences that you give it. So you’ll say, “I want to go on these rides and eat at these restaurants.” The app will say, “you should do it in this order.”
2. Allocate “wishes” to you. Those wishes can be essentially FP+, prioritized dining reservations, priority fireworks/parade viewing, etc. According to the various Disney blogs, off-site guests will get maybe 1 wish per day. On-site guests will get more, with deluxe resort guests probably getting more than moderate and value resort guests. Then you can purchase additional wishes.
Genie may be able to take your wishes into account; I’m not sure how that will work. Certainly once you redeem your wishes, I imagine it’ll update your proposed itinerary.