First of all, let the excitement countdown for your trip begin!!! We're just under 3 weeks away from leaving too, and our 3 kids are beside themselves.
Fastpass+...aka FP+...will depend on if your staying on or off property. If you stay on property, you can book up to 60 days in advance. If your off property, it's 30 days. With your situation, both of those are already passed, so you can start booking. Honestly, you may have a hard time getting on the most popular rides now, like Soarin', but you should still be able to get a lot.
I'd suggest downloading the My Disney Experience...aka
MDE...app on your phone. You can book FP+ from there, or you can do it from your laptop on the WDW website. You'll need to link your tickets to the account you set up. You can then start booking FP+ (the app and website have instructions on how to actually do it). You can book up to 3 attractions per day, they must be in the same park. You don't have to book 3, but you can only do 3 at the max. FP+ will give you a 1 hour window, for example it'll tell you to show up for the attraction from 4:10-5:10pm. So you can go anytime in that window. When you book it, you'll be able to choose from what time slots are left. Once you use those three FP+ on that day, you can then go onto the app and try to get another one.
One tip, if you can't get an attraction you really want, such as 7 Dwarfs Mine Train...aka 7DMT, keep "hunting". You can modify a FP+ selection you get. For example, say you pick 3 in Magic Kingdom, but none of them are 7DMT because they're all "sold out". Go onto the app frequently and try to modify one of your existing selections. It'll give you options for other attractions, and you can see if 7DMT is then one of them. Sometimes people cancel their reservations or change them, so it then opens the slot they gave up.
Happy hunting and have a great trip!!!