Making menus visible in blank theme

Having spent some hours in the Codex and on this forum, I want to ask a question I never quite saw asked this way:

I have a drop down menu widget installed

I have created a blank template (not child or edited existing)

I have enabled widget areas in that template which I can see and drop things onto in the admin screens.

BUT

Nothing shows up in the template. No error codes, blank headings or empty lists. Nothing where I’d expect the menus (1xhorizontal in header, 1xvertical in right sidebar, and 1xhorizontal in footer).

I have attempted to populate the header menu with example pages, the vertical menu with a search field and latest comments (none there, I know), and the footer with plain text. None of this shows up in the preview.

Is there some magic spell I forgot?

I’m running this in dev on XAMPP, so I can’t point you to my pages, but I’d be very grateful for some hints on exactly where and what code I need to place (ie, what in functions corresponds to headers, sidebar and footer).

Sorry for being a newbie numpty, but I guess it happens to the best of us the first time ’round.

Regards
Peter