I'm currently working with a talented writer and educator towards the creation of the first of three user's manuals for Manhattan, which will be aimed at helping teachers to learn the system. Manuals for students and system administrators will soon follow. Until then, what exists in the way of written documentation is provided on these pages, but note that much of it is outdated. The software has developed faster than we could write manuals to explain it. While the documentation you'll find herein is not letter perfect, it does give you a fairly good view of how Manhattan works.
Software supporting learning ought to be free.