i dont uderstand when to use most of the lua coding as functions and esleif to make a solide game!?

i dont udner stand how to use roblox lua, example i want to make a block move around like a ball , but i dont know how to make this work, do i use function or else or then and when do i use them??? please help me if there is a good course out there which learns you when to use the functions and else ect....