Click on People on the left. Click on Users tab, then on the Edit option under Quick Actions. Use the Role drop-down menu to assign the user as a Manager.
Once you have assigned the user to the role of a Manager, you can then proceed to select the specific Groups or Courses that you want them to be a manager of.
To do this, click on that Manager's name within the Users section.
Next, click on the Manager Permissions tab in their profile.
From here, you can quickly Assign them as a Manager of any Group or Course - under the "select a course or group" drop-down menu, click on the ones that you want to choose and then click Assign.
You can also remove the Manager from any courses or groups that they are already assigned to, as well as edit their permissions.