JCrypTool installation instructions are available here.
The most important resource for users and developers is the integrated online help in JCrypTool. Simply click on the question mark icon in the main menu bar to open the JCrypTool help system. Or use the context sensitive help to display short instructions for the selected part.
The most important resource for developers is, besides the online help in JCrypTool, our wiki. Any JCrypTool team member is authorized to update our wiki with new information important for other developers.
Besides these two resources, some PDF documentation is available for download.