All About Disney's Fastpass+ System
The Basics
As everyone knows, Disney is a popular destination, hosting 52M visitors each year. Needless to say, lines can and do get long. How long? Well that varies by type of attraction, popularity of the attraction, and of course crowd levels.  No one wants to spend 120 minutes in line (not uncommon for very popular rides) so to address this issue, Disney developed a fastpass (FP) system. With the current iteration of the system, many attractions have two lines - a standby line and a FP line. Standby simply means the line for the general public who doesn't have a FP for the attraction. The FP line has a controlled number of guests so those guests generally wait 0-15 minutes. Much better! Regardless of how you acquire them or whether you're staying onsite, offsite, or visitng for the day, every ticket comes with the ability to pre-schedule three FPs (per ticket day, in a single park).  When you can pre-schedule those FPs depends upon where you stay. Onsite guests and those staying at certain Disney authorized resorts in the area can reserve 60 days in advance, and all others 30 days in advance.
The Nitty Gritty
The number one tip to be aware of is that there are fastpass tiers in place for the different parks, with the exception of Magic Kingdom, and you are only ever able to have one Tier 1 and two Tier 2s for your pre-selected passes. Everyone does not have to have the same fastpass selections, if they do not want to ride the same things, but everyone that wishes to enter the fastpass lane must have a fastpass.  The only exception to this is children under the age of 3 do not require fastpasses, as they do not require theme park tickets, and can just go along with the rest of the family into the fastpass line.
Now onto selecting your fastpasses.  Here's what to expect and exactly how to navigate the system... 
1. Click the Fastpass + tab in your My Disney Experience account.
2. Click select all when your names come up (or whatever names you will to select fastpasses for).

3. The next screen shows a calendar and the parks. Click the first day you're going to work on (always start with Flight of Passage day first, followed by your Mine Train day second, and Frozen Ever After third).

4. The next screen shows all available FP options. Select 1 that you want.

5. The next screen provides different time schedules for your selected FP.  We tend to choose the one that's closest to desired start time but not before your first desired start time so you have room to maneuver.
6. Repeat steps 4 & 5 for the other two selections you wish to make for that particular date before moving on to the next day.

7. If you wish to make any changes to your selected times or attractions, click the Modify button under the attraction you would like to change. Then modify the time to what you want. Do the same for the remaining two (if needed). If you can't get the exact times you want, just be careful to avoid your dining times (if you book any dining) and choose next closest. It's kind of like one of those old slide puzzles in that 2 attractions can't occupy the same time slot at the same time. So you could have to move one out of the way just so you can schedule a different attraction in that slot. It's actually easier than this probably sounds. LOL
8. Once you have used your initial 3 passes or their times have expired, you are able to select 1 additional pass at a time right from your app. The process will look the same but you will only be able to have 1 at a time on your account after you have used your first three.
Something else to keep in mind - the time selections initially presented by the system are not necessarily all that are available. If you modify, you may see slightly different times (usually a difference of about 5-10 minutes in either direction but it can vary).
Suggesting the best use of FPs and scheduling them is a service we provide for free to our clients. If you'd like  assistance with your FPs, please contact Jenn or Nicolette regarding your vacation plans.