What does "being ONE with the Brahman" mean in fact?

Are jivas already ONE with and the SAME as It is even while jivas have their physical bodies?

Do jivas reach Oneness with it after enlighment?

What does 'advaita' (=not two) mean in this jiva (atman) - Brahman relation mean?

Is the following description true for the meaning of Oneness in advaita view:

Brahman is the Sun and jivas are its rays. So their (jivas') essence is the same and one as that of Brahman, yet Brahman (Sun) is the source, It gives the power.