This page of the wizard allows you to enable or disable specific facets that define necessary characteristics for the project. In time you switch to this wizard form, all critical facets are already checked for the chosen Dynamic Web Project.
Notice that this page of the wizard also allows you to specify the necessary version for any facet.
Moreover, you can specify your own preset of selected facets by checking needed ones in project facets window and clicking on Save button.
You can also see all available runtimes after clicking on Show Runtimes or create new ones using the New button.
Here, if more than one runtimes are checked, the Make Primary button won't be dimmed yet. So you can make use of it to mark primary runtime.
Next button will bring you to the Web Module wizard form.