Formulas for Work Center Capacities

Hi PM Experts,

Can someone explain me the whole process of defining formulas for Work Centers in relation to capacity calculation?

What I basically want to do is provide the work center avaible capacity ( 8 hours per day with 4 persons) and the system to show to what extent the capacitiy is utilized, both in text and graphical form. For this I'm using PM Orders with the above work center in the operations and I'll be scheduling the orders.