Here is some very basic stuff on the Kabbalah
The reference book is the Zohar. It was written by Rabbi Shimon Bar Yochai (Rashbi), who lived in the 2nd and 3rd centuries CE. And also written in the 11th century by Kabbalist Rabbi Moshe de Leon. This view was contradicted by Rabbi Moshe de Leon himself, who said that the book was written by Rashbi. Then it was hidden for many centuries because it was believed that only upper eschelon Jews could use and understand it.
The Zohar is a practical guide to inner actions that one performs in order to discover deeper, higher states of perception and sensation.
The Zohar is a collection of commentaries on the Torah, intended
to guide people who have already achieved high spiritual degrees to
the root (origin) of their souls. The Zohar contains all the
spiritual states that people experience as their souls evolve. At
the end of the process, the souls achieve what the Kabbalists refer
to as “the end of correction,” the highest level of spiritual
wholeness. To those with spiritual attainment, i.e. Kabbalists, The
Zohar is a practical guide to inner actions that one performs in
order to discover deeper, higher states of perception and sensation.
The wisdom in the Zohar is no more and no less than a sequence of roots, which hang down by way of cause and effect, in fixed, determined rules, interweaving to a single, exalted goal described as, “the revelation of His Godliness to His creatures in this world.” In simpler words, there is an upper, all-inclusive force, or “the Creator,” governing everything in reality. All the world’s forces descend from this comprehensive force. Some of these forces are familiar to us, such as gravity or electricity, while there are forces of a higher order that act while remaining hidden to us. Kabbalah holds the map or the knowledge of how these hidden forces are structured, and the laws by which they influence us.
It teaches us how to develop a sense of these forces, and finally, discover their only purpose – to bring us to the revelation of the Creator, while living in this world.
In a nut shell, it is using the wisdom of the Torah (presented in the Zohar) as used in everyday life.