The Details page is where you can enter all the compelling information that is going to help people make the decision to do your event. You don't have to replicate your entire website here, but at the very least put in some info in Overview and Course Description, as those are the two fields potential participants will definitely read.
HINT: If you know some basic HTML, you can use it in these text boxes. See: Can I use HTML?
ANOTHER HINT: You can not only edit these sections in Event Setup, but you can also go straight to your Event Page, click on the Details tab and edit the wording right there.