On the big scale of things, serving food is pretty simple. You are polite, you smile, you answer questions customers have about the food, you take an order, pass it to the kitchen (on paper or electronically, noting any additional requests or deletions) when prepared you check it is prepared as requested (for example, that the burger has its side salad instead of fries) add necessary or optional condiments, and deliver the food to the table. You ask if anything else is required. You check back after a short amount of time to ensure everything is satisfactory, and respond to any issues. You clear plates when they have finished, perhaps offering to box any leftovers. You offer dessert etc. and follow similar procedure. When the customer is ready, asks or otherwise indicates, you deliver the bill, process payment, and say goodbye. Drinks are a similar process, but as the comment was about food, I left that out.

There is a reason many teenagers do waiter / waitressing as their first job, because it is pretty simple to get right.