Wonder where to locate the enrollment key for your course? It’s no longer in the course settings. You need to click Users>Enrollment methods>Self enrollment (Student) to get to the page to adjust your settings.
You then can set your enrollment key and customize other settings. You may want to have your students automatically put into groups once they enroll, so enable the group enrollment feature (and of course set enrollment keys for each of your groups.)
The custom welcome message is sent to students after they enroll, so you might want to include some detailed instructions on how to get started.