intransitive to be in a position in which the lower part of your body rests on a seat or on the ground, while the upper part of your body is uprightsit on a chair/bench/stool: Matt sat on a park bench, eating his lunch.
sit in: They were sitting in a café drinking coffee.
sit at a table/desk/computer: I was sitting at my computer when the phone rang.
sit next to someone: I usually sit next to Andrew in history class.
sit together: My friends and I like to sit together in the cafeteria.
sit around: Six of us were sitting around the table talking.
sit side by side: We sat side by side in the back seat.
sit still: Sit still (=without moving) while I brush your hair, Lucy.
just sit there (=not do anything): Are you going to just sit there, or are you going to help me?