Many witches find energy to be living, so partially adds to the theory of spiritual union. Rather than manipulating it, as many such as myself could start off thinking, our bodies can be attuned to the forces of various energies, that likely reside within ourselves, and cast off the energy for a purpose, that may either be done by your subconscious or another entity or flow of energy that works well with you. The mind can trick you damn well easy, so it is almost always hard to try in the beginning.
Some types of things are either so close to magic that is referred to in other areas of study. Magic isn`t only just applicable in terms of laws, but it reflects the natural order in alot of ways, that it may be so, but try telling other people. One book wouldn`t give the whole idea, but can tap into hints of it, as far as my books have gone. A psychology book called Experiment In Depth, to me, seems like a good prefix. There is alot to learn from that book, and aside from that, its wiser to work for self-improvement, for a cautious beginning, because you don`t want primal forces of the mind to work against you in magic.
After reading that book, if you so choose, I think rootwork or herbal magic would be good on physical terms, but after reading the book, you may feel inclined to work with both the outside world and inside, for balance, and for the inside, I`d recommend learning the runes(Poetta Edda is the religious book in which they and the surviving Asatru tales are mentioned), because inside, you are working with the subconscious forces, and the runes, once understood, may become the keys to your being.