It's mostly a pretty good looking and nice feeling website, but the explanation of what it is (necessary for me to understand why I should stay) should absolute

It's mostly a pretty good looking and nice feeling website, but the explanation of what it is (necessary for me to understand why I should stay) should absolutely not be sourced out to an in page pop-up, which it both annoying and way too ephemeral. I'd suggest an info-icon triggering a top bar.