Out of the box, the plugin serves an automatic course archive at /courses/.
Using your own catalog page
If you’d rather design the catalog yourself, go to Settings, then Catalog and turn Course archive off. Then a page of your own can live at that address and be the catalog. Put [nonprofit_lms_courses] on it, or use your page builder’s posts module.
The Setup button does this switch for you when it creates your Courses page.
Changing the word in your course addresses
The same tab has Course URL base. That’s the word in your course web addresses, like /courses/course-name/. You can change it (to classes, say), but do it early. After a change, links people already shared stop working, and visitors need the new address. Update your menus and any links you’ve sent out.