There's a number of threads about this -- one forum is all about using My Magic Plus, FastPass and Tiers, etc.
Here is also a link to N&R about the new tier system at DHS. Maybe this thread and the forum listed above might be helpful. I can't speak to any of this, because I haven't been to WDW since last year. It sounds fairly complicated and doesn't seem to allow for as many fastpasses to the major attractions as before. I wish they would have just left the older FastPass system in place, or just eliminated the entire fastpass concept entirely. The whole thing seems to stress out a lot of guests, so you're not alone.
Short Story: On August 29, Tower of Terror and Rock 'n' Rollercoaster will be added to Toy Story Mania, Slinky Dog Dash and Alien Swirling Saucers as Tier 1 Fastpass+ selections. Star Tours stays a Tier 2. Smuggler's Run still set to open as a non-FP ride. I am unaware of any other changes...
forums.wdwmagic.com