I just watched the video again. It does not explain how to add users to the group. I will write a proper howto topic to explain how to add users to a group. Here is a brief overview of how to do it.
First, go to your group’s page by clicking the “groups” link in the hamburger menu, then clicking the group’s entry:
On the group’s page you can add users to the group either by clicking the “Add Members” button, or by clicking the “Bulk Add to Group” button:
If you click the “Add Members” button, a form will open that allows you to add users by their username. Start typing a username into the form. An auto-complete dropdown will open. Select the user from the dropdown:
Their username will be added to the form:
Click the “Add” button to save your changes.
If you use the “Bulk Add to Group” button instead of the “Add Members” button, a form will open that allows you to copy and past a list of usernames or email addresses, with one username or email address per line. This approach is useful if you are adding users to the group from a spreadsheet, or from results that have been returned from a Data Explorer query:
Click the “Add” button to save your changes. A message will be displayed letting you know how many users were added to the group:
In the screenshot above, you can see that one user from my list was successfully added. Two users were not added to the group. The reason they were not added is because they do not yet have accounts on the site. They will need to register on the site before they can be added to the group.