1) how does the earth wire, together with a fuse provide protection for the user when using an electrical appliance.
2)advantages for a RCCB
3) why is 3 wire system better and cheaper than 2 wire system in the long term
4) how does the fuse help and how could a circuit breaker be used
This all looks like shit you should learn in first year high school, you're probably underage.
Also just google it, none of it looks hard or something you need to ask about. Come here instead if you have more specific questions (eg. equations) you need help with, that google can't answer
Stay in school, kid. Also go to your study club or whatever the fuck.