Your capital payment is your share of the aircraft - normally bought from an existing member. What you pay multiplied by the number of Members is (hopefully) what the aircraft is worth. You should have equal rights, if you have equal shares
Any monthly, standing order payments go towards fixed costs (hangarage / parking, insurance etc).
Wet is the hourly rate you pay including fuel. If the rate quoted is dry then you pay that to the group, the fuel you pay for yourself. The idea is whatecer you pay (wet or dry) covers the running cost of the aircraft including maintenance.