First you need to sign in: https://unity.scanpower.com
Hover over your name in the top nav and select "Account" and scroll down to "Sub-Users".
To add a sub-user, click "Add sub-user", enter the login-information and appropriate permissions, and save.
To edit a sub-user, click the edit button on the row of the sub-user you want to edit, make the appropriate changes, and save. To activate/deactivate a sub-user, click the on/off toggle on the row.
The red highlight are permissions you can give each sub-user. Please note that some of them are only available at higher level plans.