Once again, answering my own support request. I've found that instead of using the SPBP component 'Add page' (which doesn't work for me at all), the best strategy is to first create a Joomla Module (tyle SPBP), choose a position, save the module, then click on SPBP Edit button. From there it's reasonably plain sailing. You see a blank page (not the home page which I kept seeing in earlier attempts using 'Add Page' from the SPBP component.)

I hope this helps anyone else having difficulty grasping how this component is meant to be used.

(Note: Since posting this message, I have found that 'Add Page' from the SPBP Component does actually work. It's just the way each new page presents itself that I found initally very confusing. I still believe, when adding a new page, I should be presented with a blank window (blank canvas?) rather than one filled with my home page content, which is not where I plan to place the new content.