Everyone has their theory, and no one seems willing to simply get people started. Following is a basic tree diagram, with planetary correspondences, and a quick discussion of pillars, a few theories, et al. I have conspicuously chosen to avoid any discussion of paths and their numbers, considering that an advanced and often unnecessary topic for those who have not delved too deep. In the interest of making my life easy, I have turned the usual circles for the Sephiroth into squares.
Ascii art is easier that way.
These can be seen as corresponding to the known planets and the Sun. In various magickal systems, a common goal is the attainment of understanding such as results from successful traveling the tree from Malkuth, or Earth, to Kether, the attainment. I realize this is at odds with many systems and presentations, which often give no planetary correspondences whatsoever for these Sephiroth. Okay, so you get the picture. Lots of interesting Hebrew names of the Sephiroth, with their various meanings and attributions according to which author you are reading, and according to the classic Jewish scholars on the Kabbalah.