OP, perhaps you've already looked at the
WDW website, but there is a lot of information there.
To add to what other posters have said, there are 3 types of LLs:
(1)
Lightning Lane Multi Pass: Covers most rides except the headliners in each park. If you're staying on-site, you can book 3 LLMPs for each day of your entire stay 7 days before check-in. The 3 LLMPs you book in advance for each day all have to be at the same park.
Every park but DAK has tiered LLMPS. You can prebook only 1 tier 1 LLMP for each day you're purchasing LLMPs. But . . . after you have used your first LLMP of the day, regardless of its tier, you unlock the tiers and can book any tier of any ride in all 4 parks (assuming you have a hopper) after that.
You do not need to purchase LLMP again for another park if you do hop. You have already paid for the LLMP. But good luck getting top attractions at a park you hop to.
(2) Lightning Lane Single Pass: For the headliners in each park (e.g., FoP in DAK; RotR in DHS). This is a separate fee from the LLMPs but you can purchase them at the same time as you book your LLMPs. You can book only 2 of these per day and of course you need hopping on your ticket in order to book in more than one park.
(3) Lightning Lane Premier Pass: For LL access to every ride in a given park. The LLPP is good for one LL on each of the rides and you do not have to book any rides in advance. But, like the LLMP and LLSP, you can ride each ride only once with the LLPP.
I have no experience with the LLPP--out of my price range--but LLMPs and LLSPs can be booked only using the
MDE app on your smartphone. You cannot book them using the WDW site on your computer or tablet. Booking starts at 7 a.m. Eastern Time 7 days in advance of your arrival at an on-site resort or 3 days in advance of your stay at an off-site resort.