How do I install and test Spirit before making the theme live?

I installed Spirit using the Dashboard, and did a live preview of the site. The site looked completely vanilla - no formatting, page graphics in line only, no sidebars, etc.
The instructions for Spirit say "If you want to try out the theme first while retaining your current design we highly recommend using the Theme Tester plugin", but I couldn't find a Theme Tester plugin - only an A/B Theme Testing plugin.
I wasn't sure if the Upfront checkbox should be checked in the A/B Theme Testing plugin setup, so left it blank. When I look at Spirit using the A/B Theme Testing plugin, it shows pixilated images, some lorem ipsum sections, and some health care language - none of which is on the actual web site.
I downloaded the Upfront Guide, but couldn't make anything there correlate to anything else I'd looked at for the Spirit child theme.
I'm trying to deal with too many unknowns here. Could you direct me to the Theme Tester plugin, and some directions as to how to use the Spirit theme?
Dennis McNeely