Do I buy food from the food counter and take it to my seat? Or will someone come to my seat, take my order and bring it to me? Would this be during the movie? Or can I only order before the movie? And do I tip the person who brings my food to me?

Yes you could do either way. I always order it inside the theater. As for Tip, I have always ordered it from inside so I Tip. But if you order from the bar outside then i don't think you need to tip as sometimes they make multiple rounds serving your food and can be a different person each time

Place an order at outside and pay and they will bring them inside to your seat.

YES you could do either way it is easy for them to come to you