In the enrollment page, and with the group view, you can click on a group to see and edit which users and courses are linked to that group. You also have many options:
Link a user- Click on "Link User", select the user you want to link, and click on "Link"
Unlink user(s) - Select the user(s) that you want to unlink from that group, click on "Unlink user", and "Unlink"
Link course - Scroll down, click on "Link course", select all the courses you want to link to that group, and click on "Link"
Unlink course - Select all the courses you want to unlink, click on "Unlink course", then "Unlink"
Manage users
Please note: You can also click on a user to see and edit which groups and courses are linked to that user