Not every ride has them, but most of the really popular ones do. In some cases (e.g,. Toy Story Mania at DHS and Soarin' at EPCOT), you will most certainly want to get a FastPass rather than wait in what might be a two hour line (or longer).
If possible, you might try to look at maps, guidebooks, YouTube videos, etc., to decide what handful of rides you definitely want to hit so that you can plan your day accordingly. As a prior poster said, you cannot just go around the park collecting FastPasses for all the favorites and then go on them one after the other. Once you have a FP in-hand, it's usually another hour or two before you can get another one. They have also recently been enforcing the rule that says you must use the FP by [whatever time] or else it expires. There was a time when you could show up hours after the expiration time and still get on the ride through the FP line....but no more.
Don't "over-plan" your day to the point of guaranteeing disappointment if and when you can't fit in something that you had planned to do, but a reasonable amount of foresight and a careful use of FPs can make your days in the parks a lot more stress-free. We have never used any of the "touring plan" websites, but there are people who absolutely love them (and I'm pretty sure they give recommendations on how best to hit the FPs, etc.).