Depending on who you ask, its either a great step forward in planning your theme park experience or an experiment gone wrong.
Information can be found on the official Disney site under My Disney Experience / Fastpass +.
There are also many great posts on the boards about the Fast pass + system, some are pro other are con, they do provide a lot of great information about the new system. The thread listed above is a great resource.
In a nut shell, the new system has removed the old paper Fastpass kiosks from the parks. Instead, each guest is allocated 3 Fastpasses per day for one park of their choice. Almost all of the attractions at the parks, parades, and shows have Fastpass availability. The Fastpasses are linked to your admission media; either a plastic ticket or a MagicBand [the media is embedded with RFID technology]. Depending on whether your staying on property or off property, determines when you can reserve your Fastpasses. * Some exceptions to testing groups.
If your staying on property, you are now able to reserve your Fastpasses up to 60 days in advance of your Resort stay through My Disney Experience Portal/App. If youre staying off property*, you are able to make same day Fastpass reservations at the park you are visiting at a Fastpass + Kiosk. These kiosks are located throughout the parks and are staffed by cast members to help in making your selections. I would advise having 3-5 attractions in mind when going to make your selections. Some parks have a tiered selection system that limits your ability to select E-Ticket attractions [can only select one attraction in the top tier].