Concept of God in Judaism?

you can generally find two basic approaches to that issue - the philosophical point of view, and the mystic-kabbalah POV.

from the philosophical pov, G-d is different than anything inside the world, is infinite, omnipotent, omniscient, his "Oneness" isn't like a regular object from which you have only one item, you cannot actually say direct things in a human language about G-d because you can't use a predicate or an adjective together with the concept of G-d and still maintain the Oneness I mentioned before. the only way to describe G-d is by using negatives - you can say that G-d *isn't* certain things, and the more the list grows, the more you get closer to understanding the concept of G-d (although the full meaning cannot be grasped by the human mind).

the type pf connection between Man and G-d, from this pov, is more logical than emotional. Man has no influence on G-d, he can only choose to adhere the G-d's teaching (according to one's faith) and by doing so living in the world G-d created in the way G-d meant for you to live. G-d doesn't "know" personally, in a manner of speaking.

The mystic/kabbalah pov sees G-d as having two basic "parts" - the first part is the more philosophical one, the infinite and not understandable or reachable by a Human. but there's another side, which has many facets within, many times in contrast with each other, that are usually referred to as "The Spheres".

Usually there is a structure of 10 spheres, each represents a different facet of "personality" in G-d, and according to our behaviour we get to see different sides of G-d, e.g. mercy, anger, love, etc.

the lower sphere is the part of G-d that humans are exposed to, but using certain techniques such as meditation or chanting or praying can let you rise up and 'connect' to upper spheres. there are many different types of relationships described and studied by mystics throughout the ages, and many different approaches to this subject exist.

the type of relationship between Man and G-d from the mystic pov is such that Man has an opportunity to influence what happens in the upper worlds by his actions in the lower world, our world. every action has a reaction in the upper world. the connection is more emotional and the experience is different altogether.

The best description of YHVH that I ever heard was simply this:

IF it were possible for YHVH to cease to exist (it isn't possible, but IF), then everything would cease to exist. That YHVH is both infinitely large and infinitely small at the same time (infinite), and that no finite minded creature could ever look upon YHVH (as a whole) from the outside, but only from a narrow perspective from the inside looking out.

Shalom . . . 

The concept of G. in Judaism is entirely dependent on the divine revelation through the Bible and its traditional interpretations. In the chapter of Creation G. uses the verb "created" three times  and "said" ten times, which in the cabalistic interpretation looks like creating the hardware and then programming the hardware using computer language. In contrast with Science, which describes the World but is not self explanatory, the Bible is not only a description within the framework of contingent existence but an explanation of existence itself as generated from the One, in the sense of an absolute and necessary Being, referring only to Himself as " I shall be the one I shall be".  In addition to programming the natural laws, the G. of the Bible also reveals the moral laws in the form of ten commandments, by which the Hebrew nation, as a nation of priests, has the obligation to enact the process of restoration (tikkun, in Hebrew) of the Earth and of Man damaged by the fall of Adam. As a result of the fall, and most of all by the process of tikkun, Man becomes like G. participating in his own creation. The Bible does not describe what G. is to Himself but describes the attributes ( love, justice, mercy..) of G. in relation to His Creation, inviting Man to imitate Him, in order to "know" Him.