you come in before or after someone ate at a restuarant, to clean off the area.
This is a question I feel qualified to answer, since I was a restaurant manager for years. Bussers or bus people (not all boys, you know) clear dishes, glasses and silverware from the table after diners leave. They wipe down the table, and reset it for the next diners. The busser scrapes the dishes, seperates the silver, stacks the dishes and takes them in a tub or cart to the dishwashing area.
They may also bring glasses of water to newly seated guests, or fetch an occasional bottle of ketchup. They fold cloth napkins and lay tablecloths in restaurants that use them. They may wash the tables and chairs, and dust the rest of the dining room. At the end of the day they vacuum or mop the dining room.
They're often also assigned other jobs like emptying trash cans in the dumpster.
Bussers are almost always paid minimum wage. In a few very nice restaurants the servers will give each busser a small tip at the end of the shift, but the tips left on the table are the property of the server, not the busser.
This is a dirty job, but really helpful job to the servers. Bussers, picks up all the dirty dishes at a table of guest that has finished and cleans it. The servers usually tips the bussers at the end of the day.