Basically, you have two things you use to get into parks:
1) Your Disney ID card. This gets you, personally, into MK, Epcot,
MGM HS, and AK for free, as often as you like, from the moment you get it until the day it expires (which is also the last day of your CP). This works the same as a normal park hopper pass, so you can get in anytime during normal park hours (but not EMH) and get FPs. As mentioned, you can't call in sick and then use this. Disney's not stupid.
2) Your blue main entrance pass. This one is more restricted: you can only use it six times, and there are blackout dates. Using it basically gets you three free 1-day passes, so you can bring in guests. Unfortunately, they hand your guests the passes
after they enter, so you all have to show up at once for the first place you go that day, and they have to be used that day (so there's no way to, say, get three one day and save them, and bring in six people the next day). But I have good news:
I just saved a bunch of money on my car insurance by switching to GEICO once you have the passes, they work exactly like normal 1-day Park Hopper passes, so your guests can go to other parks on their own and get FPs and such.
At times Disney may send you a card which is basically an extra day for your blue pass. This will have different blackout dates, and if you're like me, then they will send it to you really late and you won't actually get any use out of it.

Despite this glitch, I found that the system overall worked pretty well.
If you want to bring in more guests or bring them in on more days, you can also buy tickets at a discount.