Brahman is the collective soul and matter. Brahman is absolute, infinite and eternal. It is beyond the intellect and mind. It is the source of the being intelligence and bliss. Atman is the absolute consciousness in the individual. Atman is unchangeable. It is part of Brahman, thus it has all the qualities of Brahman.
Upadhi means identity. Like the body is the identity for the soul, we can not recognize each other without the body. Our Upadhis are the body and mind. They are limited and they veil the consciousness.
Maya is the illusion. Maya is the veiling of the truth, it covers the real and gives the illusion of reality e.g. in the darkness, a rope lying on the ground may be mistaken for a snake. But in light we know that the rope alone is real, not the snake.
Avidya is the ignorance. Maya manifests in the individual in the form of avidya (ignorance). It keeps us away from seeing the truth.
Ishwara is the highest form of god one can think of in the material world. This also corresponds to the personal god or belief. Swami Vivekanada said "Ishwara represents the highest concept a human mind can hold and the human heart can love".
Jiva is the individual soul. It is the self identifying with the Upadhis. Jiva believes itself to be bounded and limited by upadhis thus consequently suffers. Jiva has to born and reborn again until realizing his true nature again.
Q 1. What is Brahman and Atman?
Q 2. Define how Maya and Upadhis are related to each other?
Q 3. How Brahman is different from Ishwara?