Vedanta is a "nondual" tradition from Hinduism. It is similar in many ways to other nondual traditions like Zen or Dzogchen Buddhism, Taoism, Christian Mysticism (Gnosticism) and Sufism from Islam. Advaita is a "sect" or branch of Vedanta which says that there is a singularity of reality, a "Oneness" or one essence underlying all that appears to be.
Advaita means - not-two. This is not a path, not a practice. Advaita is a direct description of reality as it is.
Vedanta means - the end of the Vedas - the end of all knowledge - unlearning - not-knowing. Through investigation into the nature of Reality, called "self-knowledge" - the seeker comes to the realization of the nondual nature of Reality.
Advaita Vedanta does not seek to impart a new set of beliefs, but to rip the rug out from under all beliefs, all assumptions, including the assumption that there is an individual entity or person who exists, who was born and will later die.
In the direct recognition of Reality as it is, the seeker falls away as the root or foundation of all false translations.
Our Problem
Our problem is that we feel limited, we feel isolated and small, temporary, insignificant. Therefore we seek to fill that hole with either things from a material standpoint or states from a spiritual standpoint.
Yet it is this inherent feeling of limitation from which we cannot escape. My belief about myself is that I AM limited, therefore to seek the limitless is always quite frustrating. If my belief about myself is true, if I am in fact limited, if reality is in fact made up of separate existences, then spirituality really is a fantasy. This means that bondage and suffering is the truth of existence.
Yet there is another possibility. That possibility is that I was never limited to begin with, reality was never made up of separate existences. If that is the case, then the only problem is my own ignorance of myself, ignorance of the truth of reality as whole. That ignorance can only be corrected by knowledge of myself, of reality as it truly is. Vedanta is a means of knowledge to know myself.
Paradox
The "seeker" and "realization" cannot co-exist. As a seeker, taking yourself to be an individual "part" of the Universe, you have set up a lose-lose situation. A seeker can never find Oneness, because it is the very idea of a seeker which automatically excludes Oneness as a possibility. It is the concept of a person which is, by definition, the core limitation.
So asking what can I, as the seeker, do to realize Oneness, is futile. It will always be futile. The "seeker" and Oneness are mutually exclusive, we might say. It is only when the very root concept of the individual, the seeker, the person, is questioned, that the opportunity for Oneness or realization can come.
The Subject-"I"
Vedanta asks nothing of the seeker but to inquire into the sense of "I", the subject, Atma it is called. Is the world "I"? What is the world made of? How does it appear to you? It comes as sensory input, objective experience. Yet isn't this the same with the body? Is the body "I"? What about thoughts? Are thoughts "I"?
No. The body is not the subject, as it appears TO the subject-"I". Thoughts are not the subject - thoughts appear to the subject-"I". Any feeling, memory, emotion, sensation, perception, concept, idea - all are objective content to the subject-"I" which you are.
So what IS that subject-"I"? Any sensation is not it. Any perception is not it. Therefore that subject-"I" is without form, not objectifiable in any experience. Yet it is ever there - undeniably. You are ever there for any and all experiences. That subject-"I" is not, in fact, a body or a thought. It is the noticing of the body, thoughts and world.
Is it not true?
Therefore that subject-"I" is pure, without the first attribute, no shape, size, color - no dimension in space or time. What you truly are, in actual experience, is not something which has any objective content, yet it is the most intimate aspect of all experience.
Another word for the "subject" is knowing.
The Dissolution of the Seeker
The goal or aim of spirituality as seen in Vedanta is not the attainment of enlightenment for the seeker. It is the freedom FROM the seeker. That Oneness or one essence is actually what you are - only you have bound yourself to the idea of a limited being. In questioning this idea, you come to know yourself as you are - the whole, the totality, no longer imagining yourself as limited. This is the only goal.
Yet as you are already that totality, this limitation or bondage is only conceptual - the so-called veil or "maya" is only made of concepts. There is no actual separation or limitation in that one essence, even as it appears to be everything.
Therefore enlightenment is simply the recognition that you already are that one essence, and never were bound at all. You are only being as you already are. Free, perfect and whole.
Existence
If I say "I am seeking" I have asserted myself as an individual existence. I take my existence to have begun on a particular day and a particular time. When I say "I" I really mean "a separate existence" - I really assume that existence is separated, that there are "Things" which exist on their own, apart, standing on their own. What I really mean is that each "appearance" has it's own existence, that it's existence began and will end. My root idea about reality is that it is composed of an infinite number of existences. It is this idea which is called "bondage".
Vedanta calls "appearance" mithyA - mithyA means that which comes and goes, that which appears, that which has no existence on it's own. A "thing" is only a thing from a particular viewpoint, only available via a particular means of knowledge, a particular means of measurement. If that means changes, the appearance changes. If that appearance changes, nothing happens to the "existence" of that "thing". Existence is Sat - Sat means - that which IS - Sat just means "IS". There is what IS - Sat - and THAT appears in various ways depending on the means of knowledge or measurement.
There is only Sat - mithyA is dependent on Sat yet Sat is not dependent on mithyA - what appears IS Sat. Sat is Brahman - the truth and reality, the "one existence" which appears or expresses as everything.
Therefore what I am is Sat - that which IS - that one existence - one reality which appears as everything. I cannot fundamentally find any division between what I am and what appears, unless I take mithyA to be absolute reality.
The realization of what I truly am is expressed in the equation - Tat Tvam Asi - You Are That. The realization is that what is called "Brahman" IS the whole reality itself and if I am anything, I am Brahman. I am that one reality itself.
A Metaphor
The gold Chain is suffering - it is seeking Peace and Happiness - it seeks to know what it is, truly.
It meditates - hoping for some vision or special experience of Gold. it's essence. It visits the Guru, asking for guidance to know what it is.
At first it formulates many ideas about Gold, what it must be like, feel like. It desperately seeks to know it's essence of this Oneness called "Gold".
Yet at every turn comes frustration. No vision or experience comes, or if they do come they always pass. No lasting realization of Gold has come.
The Guru says "what you are IS Gold - you cannot SEEK it for you ARE it." The chain is baffled by this paradox and glosses over this wisdom, seeking out Guru after Guru. book after book.
At some point the chain has exhausted all avenues, burned through all concepts about Gold. Gold cannot be found no matter what attempts are made. No concept brings the Peace and Happiness being sought after. The chain is lost without a foothold, Gold is nowhere in sight.
Yet the Guru only smiles. For in reality there never was a chain outside of a form of Gold itself. It was never chain seeking. Chain was a shape of Gold, a manifestation of Gold itself. Chain's only existence was in a concept - the reality always WAS Gold itself. Chain could not find Gold after all.
It was not chain which realized it was Gold. It was Gold which realized it was never "chain".
Right now, you are the totality itself, the one essence - you have taken yourself to be a limited entity, like the chain. As that entity you feel limited and need to seek the totality. Yet that entity you take yourself to be is only a name, only a form, only a manifestation of that One Essence.
Therefore this "I" can never find anything. "I" can never find that essence. It is that essence which realizes it never was that limited "I".