With an ADR, you have the option of pre-ordering which gives you the opportunity to go in a shorter line to confirm your order and pay. You then find a place to sit and wait for your food to be brought to you. You can skip the pre-ordering, but the line for people not pre-ordering is usually much longer. The process is similar. You order your food, pay, and go find a seat. Your food will be brought out to you. Without an ADR, you won't be able to eat there at all.