I am so old school that I don't even know what the plus is? And what are tiers? Now I am getting stressed. I just want to be enjoy my vacation!
Don't worry, don't stress. It's not that big of a deal. With the old FP paper system, you had to walk, run, stampede to a kiosk that was physically at the ride itself. You put your ticket in and it spit out a paper ticket that had your FP on it and told you when to come back. First come, first serve. For popular rides, like TSMM, if the park opened at 9:00am, by 9:30am the first FP available would be for 8pm. So you had to come back 10 hours later to get on the ride.
The current FP+ system does everything electronically. Either 30 or 60 days out (off site or on site, respectively), you can log onto
MDE and pick your FP+, as well as a time slot. Again, it's still first come, first serve. The system opens at 7am (unless it changed recently). So if you're on site, at 60 days from your first day in the parks, you can log on and pick a ride and a time. If all the spaces for that given time are gone, you'll have to pick another time. But unlike the old paper system, which just went chronologically, you can pick your time. You can pick 10:10am, you can pick 2:40pm, etc...assuming that slot is still available. You can pick up to 3 rides to FP+ per day. They must be in the same park, so you can't do one in MK, one in Epcot, etc...
The tier system is in use in most parks now. It puts the rides into groups. Typically the most popular rides are put together in one grouping. Call that tier 1. Then the others are in tier 2. You are only allowed to pick one ride from tier 1. The other two FP+ must then be from tier 2. After you've used all 3 FP+ that day, you can log onto MDE and try to grab another FP+...it can be tier 1 or 2. Of course, you're subject to whatever is still left for that day...but honestly you'll still find a fairly decent selection. Maybe not THE top rides, but typically something fun is still available.
It's not as complicated as it sounds. Once you use it once or twice, you'll quickly get the hang of it.