It depends on the campus board setup. Nice setups often have:
- The campus boards on an over hang with wooden slats underneath for your feet.
- And various sets of grips. The easiest is very positive and the hardest probably has nothing to wrap your fingers around at all.
The slats help you scale down the exercises so you don't have to do them legless. So you can start using them now.
Then you really just do patterns. Starting with both hands on the same rung:
- One hand up, match, other hand up. Go as high as possible, remembering to have enough energy to come back down. Come back down the reverse way. One hand down, match, other hand down.
- One hand up, match. First hand down, match. Repeat.
- Keep one hand on the same rung. Move the opposite hand up one rung. Keep moving the same hand up until you can't go any higher. At your limit, cut loose with your feet and then put your feet back on the same rung. Match your top hand with the lower hand directly. Do other side.
- Reach up with one hand as high as possible. Then campus down with that same hand until you match on the starting rung. Do other hand.
- Lots of other ideas and patterns ...
Then you can just add variations as you get better. For example, with the first pattern, go up 2 rungs or go up in a pattern 1 - 2 - 3. When you are even stronger, go legless.
A good resource is the book "Gimme Kraft".
Kraft is german for strength or power.