ref all home is setting the machine zero, if you don't have home switches you set it to a safe spot or front left corner with Z at it's top height all it is, is a spot that you decide is home, machine zero.
mach3 is a dumb system as in you tell it what to do, BS is ball poo
yes once you have set home (machine zero) you have to set work zero what is where your material you are cutting is