Click on Employees from the top navigation bar. If the person is not listed as an employee, add them by clicking on Add Employee. Once the employee is in the system, click on the Groups button in the top well.
The Groups page allows you to view your current groups and who is currently managing them. Click the Create Manager button and select the employee you wish to make a Manager. Enter their email address and click the Create Manager button.
An email will be sent to the Manager, inviting them into the system. The Manager will create their own password. The next screen will allow you to assign the Manager to a Group.
A "Pending Invitation" message will appear in the Account Panel until the Manager accepts your invitation.