I copied a picture from a previous post and marked it up to identify what I think are the key brake components.
There is only one brake for the rear axle itself.
The vertical lever will push on a pin which pushes the brake pads within the caliper against both side of the disk which can float a bit.
There will be a screw with a lock nut that is what you use to tighten up the brakes. If the pads are completely worn out, which is unlikely, removing the caliper and installing new ones is easy.
Have someone apply the brake while you watch at the rear and you will see the lever move and press against a pin.