Users' Manual

As you may know, there is no suitable template on the web site from which you got templates for the PMP, SDD, etc.  Therefore, you may use whatever format you choose.  Regarding content, I have only a few expectations:
 
bulletI would like to see your UM divided into two parts:  a tutorial part and a reference part.
bulletThe tutorial part should use an extended example which exercises most (at least the most common) functions in your software.  Typically, if a function as several options, your example should demonstrate some of them.  The tutorial should include screen shots of your application to support the narrative text.  If you application is not yet suitable for producing screen shots, then just produce the narrative text as you expect the application to operate and leave place holders (empty figures) for the screen shots.  You do not need to draw figures to replace anticipated screen shots; however, your narrative text may need to more precise to convey a meaningful message in their absence.
bulletIt is acceptable, though not required, to replace the tutorial part of the UM with a web-based tutorial.
bulletThe reference part should be organized according to function.  For example:  assuming you have a typical menu bar, you would cover all the "File" menu options in one section, the "Edit" options in another.  I suggest using the linux man page format for these reference pages, e.g.,
bulletCommand name and synopsis
bulletDescription of command and options
bulletExamples
bulletRelated commands or functions
bulletFootnotes (if applicable)
bulletThere is no length requirement for the UM (or the maintenance manual or installation manual for that matter), as long at it reasonably covers the ideas above.