I've learned that some people like to do theirs on the computer and just save it on a floppy disk. Some buy expensive leather books with blank pages & write on them. Some (a lot actually I think) just use a 3 ring binder so you can redo pages when needed.
So your probably asking...What goes inside? ANYTHING you want. Recipies, rituals, color charts, lunar charts, tarot reading descriptions, sketches, feathers, etc. Anything you might want to refer back to at some point & won't want to spend a ton of time digging to find. ,br>
You put in whatever you may feel is important and you want to keep. Also so that way you don't have to go digging through things to find what you were looking for. I like the Leather book but the 3 ring binder approach isn't bad since you can always redo pages you goofed on, whereas the purchased books you can't, the goof will stay there unless you cut the page out. But thats your choice to decide!