There are no paper fastpasses anymore. It is all electronic, or FP+. You are able to schedule 3 ahead of time or in the park. In both cases, you can choose from what is available. After the initial three have been used, you can schedule additional FP+ one at a time.
In park FP+ are scheduled at any park kiosk, you don't need to go to a desired attraction.
In regards to SDMT, that is currently the most sought after FP+. So, it is often difficult to get past the 60 day mark.