Bleachers are benches with no back or arms, usually in rows, where people sit to watch sports or other events.
Bleachers are where people sit to watch things, like sports or concerts.
Examples:
We sat on the bleachers to watch the game.
The bleachers were full of people.
She likes to sit on the bleachers to cheer for her team.
The bleachers were so full, I had to sit on the ground.
The bleachers went on and on, full of people.
The bleachers were like a big, long bench.