pull up a chair
1. expression Come sit with us. (The listener may not have to physically move a chair in order to join the group,) The meeting's just getting started—pull up a chair.
2. verb To move a chair in order to sit with a person or group. I pulled up a chair and joined the others at the conference table.
Pull up a chair.
Please get a chair and sit down and join us. (Assumes that there is seating available. The speaker does not necessarily mean that the person spoken to actually has to move a chair.) Tom: Well, hello, Bob! Bob: Hi, Tom. Pull up a chair. The three men were sitting at a table for four. Bob came up and said hello. Bill said, "Pull up a chair." Bob sat in the fourth chair at the table.