Ghandi

Aum (also Om) is a mystical or sacred syllable in the Hindu, Jain and Buddhist religions. It is placed at the beginning of most Hindu texts as a sacred exclamation to be uttered at the beginning and end of a reading of the Vedas or previously to any prayer or mantra and also is said in the beginning of any puja (religious ritual). The Mandukya Upanishad is entirely devoted to the explanation of the syllable.

three ways

Upanishad

"Brahma Veda Brahmaiva Bhavati" Mandukya Upanishad.

One who knows Brahman, becomes Brahman.

Many upanishads maintain that there is only one entity in the universe constituting galaxies, stars, planets, animals, humans, vegetation, and non-living things. Nothing other than that exists. So humans too are Brahman. The difference is in realizing this. One who realizes, sees that he/she him/herself is none other than Brahman.