Bramh is uncaused, eternal cause of everything, platform on which everything resides and dissolves into(in the end.) Bramh has two supreme qualities: creating and protecting everything created.
Parmatama has more qualities—he has forms and he is the greatest personality from which infinite universes come into existence.
Bhagvan has greatest number of qualities. It’s impossible to estimate his qualities or his true form. He is Parmatma, Bramh and supreme personality of Godhead Shri Krishna. He incarnates in human form and enjoys his divine Lila and does his own Bhakti.
Most of the branches of Philosophy(Indian system) emphasize on getting rid of suffering but Vedanta suggests that aim is to get Rasa(Ananda/Bliss) and Bhakti is established as supreme way.
The way to know Bramh is Bramha-jnana.
The way to know Parmatma is Yoga.
The way to become one with Bhagvan is to get his mercy and that is possible if you surrender to him and ask for his favor with humble prayer, chanting and sankeertan.
He clarifies that Bramh resides inside Bhagvan Shri Krishna.