Do you have to reserve seats

Yes. Best to reserve online or on their app. If you wait to get to the theater seats may not be available.

Yes. You can do it online prior to going to the theater on the AMC website or you can reserve a seat when you get to the theater.

All their seats are reserved seats. You pick the seat you want. I think there are also seating algorithms in the online app that will not allow you to pick two seats together that will force an empty seat between you and the next group of two seats to prevent wasted seats, but that was when it was a Carmike theater. No word on what AMC has changed.