Brahman is God (or the impersonal aspect of God) and Brahma is a creator god who exists only in the material universe.
In Hinduism we must always distinguish between God and god as God refers to the One supreme Creator buts gods are created from Him.
So Brahma is a god, not God.
But Brahman is God, or an aspect of God, depending on which Hindu religion you ask.
Thanks for explaining to me.