A new group can be set up in one of two places.
If for some reason you wish to limit or control the number of students in a group then setup the group using the menu item Uncanny Groups->Create New. The logic is similar to that described below but with the addition of specifying a total number of seats (students).
In all other cases groups will be added or managed from LearnDash LMS->Groups.
To add a new group click on ADD NEW button found at the top right of the groups page.
Give the Group a title. If you were creating a new group for students to do Certificate 1 at Victor Harbor High School we would suggest a title like Certificate 1 – Victor. The group needs to be easily identifiable to those administering the system and also to the student. This group name is shown to the student on their my courses page as shown.

Once a title has been chosen a you can add a little content to make clear who this group is for. At this point this content is not used on the front end of the site.
Settings tab
On the settings tab change Group Content to only visible to enrollees as shown below

Double check that the Access Mode is set to Closed.

All other default choices should be correct on this tab.
Courses tab
Click the Courses tab
Add the courses that are applicable to this Group.

Do not add any courses under Group Courses Auto Enrol.
Users tab
Under the Users tab users and group leaders can be added if they are already in the system.
New users are better added either manually through new users or imported from a csv file. See the help instructions for these methods.