after i draw something, i want to create a new file and erase all existing things on screen.
i can not find new on either file or document , like in photoshop,
how can i do that in zbrush?
Short answer Ctrl+n will clear the canvas. Does seem a bit funny about their implementation. But you can save projects, tools, lights, curves and many wonderful things. Image files and alphas in various formats. Reading a bit more could be helpful.