Being is the simplest way to describe existence ("what is"), and the means by which existence itself develops. For idealists being is essentially ideal, or "heavenly", while for materialists, being is essentially material, or "actual".
Hegel's Phenomenology of Spirit chronicles and critiques the entire history of scientific (philosophical) thought, beginning with the thought of being itself ("being is") and revealing the development of this most basic notion into absolute knowing, or the highest, most developed form of human thought. In his following work, the Science of Logic, Hegel explicates the features of absolute knowing and dialectical ("scientific" or "speculative") thought.