My own PHP script with WordPress Header/Footer?

(Experienced developer, but WordPress and PHP newb)

I need some help with a simple concept:

I have a PHP script called by a selection form in WordPress. The script opens a database and creates a table of data. That part works. I need to put my theme’s header and footer at the top and bottom of the output page, wrapping the table.

I’m guessing that I need some simple “require” statements that call in the WP header & footer… or maybe use of some “get_footer()” type calls that I found when searching, but I’m having trouble ferreting out the specifics.

Also, I assume that the directory structure comes into play here when calling from a script in one directory to the WP modules…

FWIW, WP is loaded in the root directory of this web site. The PHP is running from a sub directory off the root.