The Kabbalah has an elaborate metaphysics that is based quite strongly in the neoplatonic, tradition. Middle Platonism posited four worlds of reality which are reflected in kabbalah's four worlds. The One, Mind, World Soul, Material World, which correspond to Atzilut, Beriah, Yetzirah, and Asiyah respectively. Platonism is discussed fully, openly, and academically. Kabbalah is less so, so it's easier to explain the Platonism, and then return to Kabbalah.
The One is a transcendent unity that is the source, and cause, of the world's oneness and is the primal cause that causes all other things. Most would call this G-d. In Platonism, absolutely nothing can be said about this because it is "above" the intelligible world. The intelligible world starts with the Mind, which creates all the forms, i.e., things that can be known. So the idea of rabbit is not known to the One, but it is known to the Mind. This is important, The One is entirely unaware of any level below it. It is not intelligible, and it does not know anything intelligible. If it did, according to the Platonists, it would be a multiplicity. The Mind "emanates" the World Soul. The World Soul takes the individual ideas in the Mind and combines them to form the Material World, which it causes to exist. So, the World Soul is the "form" of the Material World, and the Mind is the form of the World Soul, and the One is the form of the Mind. So everything is an aspect of the One without actually being the One. Developments in Neoplatonism complicated this slightly by putting in middle terms between each of these four worlds, which roughly correspond to the Tree of Life.
So, starting from the top. Ein Soph is the One. You do not direct your prayers to Ein Soph. Ein Soph is exalted beyond this World and is unconcerned with it. The Mind is the ChaBaD sephiros, that which is technically intelligible. Keter forms the middle term. The idea of a numerical one is intelligible, and it is one, but the One isn't numerically One. It is one only insofar as it is not a multiplicity. ChaBa is Wisdom and Understanding, the Mind, and Daas is the middle between the Mind and the World Soul. Daas is knowledge of what exists, more concrete mental activity as opposed to the more abstract notions of Wisdom and Understanding. The World Soul is represented by the "Tipheres Circle." Tipheres represents the balance between Love and Power (or expansion and repression) and the forces of nature (Netzah and Hod, the "hands" of G-d). This is the form of the World. Blessing "flows" downwards from the One in the form of continued existence. This "circle" emanates the Material World (Malchus) in its image (Yesod which is the link between the two), and changes in the Material World affect changes in the World Soul since they are intimately linked. Theurgy, or the manipulation of the Material World in the hopes of affecting higher worlds, finds its manifestation in Kabbalah as a reinterpretation of kavanah, which is defined in Kabbalah as the meditation of the intended spiritual consequences of performance of mitzvos.