Before posting questions, take a moment and read through the documentation. It is available here
probably want a sticky for this one 
There is also the online documentation at http://www.pixologic.com/docs/index.php/What's_New_in_ZBrush_4
The online docs are continually added to and updated.
Is there no actual searchable user manual?
These docs are great if I want to read 200 pages and stumble across some info that might be useful but nothing beats an indexed user manual.
I find myself posting the dumbest questions on these forums and waiting a day for a response to stuff that could be solved in thirty seconds with a good manual.
The online docs are searchable, though bear in mind that you may turn up information that relates to earlier versions (yes, a big overhaul is necessary).
You can also search the PDF documents using the Adobe Reader search function.
Also, I have been answering questions on ZBC for several years and I still learn things from answering, so post away. 
I’ve been waiting two days without a response for an answer to a very simple question about displacing along an axis as opposed to the surface normal and have not been able to find an answer by searching through the online docs.
-=CC=-
Hey Magilla.
I know this is two weeks late but I saw a useful tip in a tutorial where using the picker you can change the orientation of the brush so that you can plane off at any angle you want. Not sure if that helps you?
thanks fizzy - I did find that as well. I’m straining to remember two weeks ago but I think the problem with that option is that the angle is relative to the viewing plane so its not a constant direction to the object space.
Ah I see.
got it
You’ll find pdf documentation in the “Documentation” folder of your ZBrush installation. There is also online documentation as indicated in the third post of this thread.
The use of the term ‘tool’ is because of ZBrush’s history - it didn’t start as a 3D modelling software and still isn’t solely a 3D modelling software. ‘Tool’ does not just apply to meshes but to a variety of 2D, 2.5D and 3D items in the Tool palette. ‘Tool’ is a generic term that I imagine was chosen because it can be applied to these items in an unambiguous way. As far as I remember, the only ZBrush-specific term used in the documentation is ‘pixol’, used to define a pixel which can hold depth and material information as well as color. Again this relates to ZBrush’s origins as illustration software.
Most people find the ‘getting started’ videos and tutorials a good place to start, whether they have experience of traditional 3D apps or not.
HTH,
Thanks