Go to Marleybone and see Babbage Basset. He is in front of a tower in front of the Royal Museum. He gives you an initial spell and the lever (now you have two) and general instructions. He sells additional spells and magic items. It comes with a castle magic help tome--a floating book. The book has to be placed to read it. I put mine near where I placed the lever. Have fun. Good luck.
Go to Regent Square in Marleybone and, over by the Museum, you will find a dog who will teach you Castle Magic and sell you everything you need. He'll start you off with a quest that will give you a lever, a couple of spells, a statue, and a brief tutorial on how to use them.
Alia Misthaven