A full admin has access to all site areas, setup, financial, household, etc. They can fully alter any of the data that the system can alter within those areas.
To add a Full Admin user, from the navigation, select Settings > Permissions > B. There you will find your list of Roles. Click on Full Admin Access. Then select Add User to Role.
Add in the user's name and email address. Next, you’ll see the full set of permissions listed here—these shouldn’t be changed. If you want to add a different type of role, click Back and then select Create New Role.