In person , or by phone
If you mean food, you tell the waitress. If you want stuff from the store, tell the cashier or go online.
You can call the store and place your order if you want to carry out, or you can go in and tell the register you have a carry out or to go order and a server will come take your order.
If you are in the store you can order once you are seated at a table. A server should be available to take your order. If that is not the case you may want to speak with the manager.
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