The Club Constitution contains the rules under which the club itself operates. In other words, who can join, how the finances are organised, what meetings will be held etc.
The Club Rules govern the conduct of flying on the Downs.
Please take the time to read both.
In addition to the Club Rules and Constitution, there are local Byelaws which regulate every activity that takes place on Epsom Downs. The byelaws contain sections dealing specifically with model aircraft. You should at least read these sections, even if you don't read the whole document.