How does the electric distribution panel work?

It's basically a system of circuits. The power from the mains enters through the input terminals. It's then split into various load circuits (5 amp for lighting, 13 amp for sockets , 15 amp for the immersion heater & 30 amp for cookers). Each of these circuits has it's own circuit breaker, which cuts the power to that particular circuit if the current draw exceeds the rating of the breaker.