Keep it very simple at first. It's common (but maybe not natural ;) ) to think linearly. If x changes then y changes proportionally. (y=mx+b)
But that's a simplified version of reality.
Maybe using ideas like: If I go for a walk in the forest, the forest affects me. It makes me feel calm, I can see the beauty, etc. But I also affect the forest. When I am there, fewer animals are in my vicinity. I leave foot prints, and maybe eat berries so that there are fewer for the animals.
I think starting with this give and take sort of idea can provide a foundation.
It's just a small step to: the system influences my behaviour and I influence the system through "these" real things.