To arrange for someone to sit in a particular place. The usher seated the guests at the wedding.
To provide seating for a certain number of people. The restaurant can seat up to 100 customers.
To install someone in a position or office. The committee will seat the new board members next week.
To fit or rest securely in a particular place or position, or to cause something to do so. Make sure the lid is properly seated before turning on the blender.