On your brakes, if you have never worked on brakes before, and don't know how to work on them, don't mess with them. Take the trailer to somebody that knows how to work on them, and watch them. Ask questions. Take notes. Once the other person takes the drums off, you can ask them what this or that part is, and how to adjust it or make sure it works.
If you do it wrong, you run the risk of not only having brakes that don't work, but possibly not being able to stop in an emergency, or having the brakes lock up while driving.
Now that you've been warned, if you're still with me, this is how trailer brakes operate, and how to adjust them:
When you step on the brake pedal, the brake controller sends power to the brake magnets, which are then attracted to the side of the brake drum, against a machined surface. Mechanical friction of the magnet moves a lever that goes from the magnet to a spreader bar between the brake shoes, at the top. The brake shoes then move outward against the drums, and mechanical friction slows the wheel. When you relese the brake pedal, the brake controller stops supplying power to the magnets, which release, and the brake shoes return to their normal resting position with the aid of return springs.
Adjust the brakes by spinning the star adjuster located on the metal plate behind the brake drum, this is the backing plate. You will see the brake magnet wires leading into the backing plate. The star adjuster can be spun by sticking an adjusting spoon (special tool) or a flathead screwdriver into the hole at the bottom of the backing plate. The hole is usually blocked with an oval rubber plug. The adjuster is positioned at a 90 degree angle to the wheels, so you would stick the tool in, and move it up or down to adjust the brake shoes. Adjust the brakes until the shoes drag, then reverse the adjustment a couple of turns.
The tire and wheel assembly will need to be off the ground to do this.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.