A bench is a long, flat seat that can usually accommodate several people. A city park bench is a nice place to sit and eat a sandwich.
A picnic table often has benches, and a bench is where baseball players wait for their turn to take a swing at the ball. You might have a work bench in your garage for gluing model planes together. A judge's symbolic office is known as "the bench," and to bench an athlete is to make her take a break from the court or field — if she has to do this often, she'll be known as a "bench warmer."