Can someone please translate this into an explanation for Dummies ( see attached screenshot )
It just means that auto-caching has been turned on. I think this always happens as part of the upgrade process. You can turn it off by going to Design>Themes and where is says “Rebuild Cache Automatically” in the top right, toggle the switch “off” (it's currently on).
From the reference guide:
CS-Cart Documentation — CS-Cart 4.15.x documentation
Here you can also see the Rebuild cache automatically selector. Click (On) if you want the modified files to be re-cached on the fly.
Thank you very much guys.