The various truth assignments don't modify the proposition "If there is God, then there's a human"; they're assignments to whether or not there are gods or humans, and the truth value of A ⊃ B represents whether or not the hypothetical world being described — with or without gods, and with or without humans — is consistent with the statement that if there's a god, then there's a human.
It might help you to rephrase this as "There is God only if there is a human", which is equivalent, and can be easily understood as a constraint on the conditions in which God can exist.
A=0, B=0 ⇒ there's no God and no human; as there's no God, the constraints on its existence is not violated, so A ⊃ B = 1.
A=0, B=1 ⇒ there's no God, but there are humans; similarly to the above, the constraint on God-existence is not violated, so A ⊃ B = 1.
A=1, B=0 ⇒ there's God without humans; this violates the constraint, so A ⊃ B = 0.
A=1, B=1 ⇒ there's God, but there are also humans; the necessary condition for God's existence is met, so A ⊃ B = 1.
In the first two cases, A ⊃ B is often described as vacuously true, as the premise of God existing is false in those cases — equivalently, the condition which is restricted by the consequences fails to hold anyway, so the constraint is satisfied by that very failure.