Yes, as ZN said there are machines near the rides.
A few tips: Unless you booked through
AAA and are staying on site you're limited on the number of FP you can have at a time. There will be a return time on the pass, it will be a one hour window. You can actually return anytime after the start time, dont worry about the end of the one hour window.
Space Mountain will run out FP first, so be sure you get them early in the day.
If you are traveling with children that have tickets (over age 3) but arent going to ride, you can still get them a park hopper- and someone else in the group can use it later. If you have children that arent riding ask for a child swap pass at the enterance. One person will wait with the kids, the other will ride the ride using the fast pass. When they comeout the other person will enter through the exit and ride. They may take someone with them. If you have two adults, and both got FP, you can do it more then once- the 2nd person riding wont use their FP at that time, they'll use the child swap pass.
Try to remember to get another set of fast pass as soon as you reach the time at the bottom that says " you may get another fast pass after ____". It will either be 2 hours after the last one or when the return start time comes up- which ever is soonest.
Better to have FP that you dont use then to have to wait in long lines!