help for electrical computation!

hiiii, been working as an apprentice and dito kami litong-lito. pinapasign din naman sa electrical engineer, but yung initial computation ng load kami yung nagawa since kami nagdedecide kung ilang lights, outlets, etc. can someone explain yung whole computation ng electrical load? paano madedecide yung size ng ground wire? pati na rin yung AF and AT? huhuhu heeelp para iwas stress na rin kay EE and Ar. huhu, thank yoou!