What can i expect to be doing if i am basically a servant at a cocktail party?

You may be asked to walk trays of food/appetizers through the party. If so your job is to discretely walk among the guests and quietly ask if anyone is interested in the food. Focus on groups gathered who may not notice you passing by. Do not interrupt the conversation, but quietly offer your food. Try to make sure you get to the whole room. Sometimes it is easy to empty your tray with the groups closest to the kitchen, be sure to make the food available to those who are at the farthest corners of the room.

You may have to watch the food display to be sure food is plentiful. Guests don't like to take the last of anything, but if it looks full they will help themselves, so you need to refill items that begin to look empty.

You will very likely have to wash and dry the serving dishes/utensils as they are emptied, and keep the food prep surfaces clean and clear.

It isn't particularly demanding physically, but it is very important to be polite, discrete, and conscientious

Picking up used cups and utensils and sending them to the kitchen to be washed. You might be asked to pass around food on platters.

serve people