The Structure of the English Competition

I wish to know (and I am sure someone can help me) how English Rugby is
structured?
In that I mean, other than the ZP, what other competitions are there? and do
the ZP clubs have teams in a local competition as well?
Also, do under 19's and 21's have a division with the ZP? or do they play in
the local comp?

Interested to know how it works there
-Regards

Ray