Often the default user roles in the system are not sufficient for your agency. You may wish to grant particular privileges normally only afforded to agency managers to some of your most trusted staff members without going so far as to give them full system access. In this case you can create a custom role.
You can create a custom role via Account Settings > User and Roles > Roles.
New roles can be added by either creating a new one from scratch by clicking Add, or more often than not they will be just involve some changes to an existing role. To create a new role based on an existing one view the role you wish to clone and click Duplicate. This will display a form where the existing privileges can be edited and a new role name specified. Tick or untick the relevant privileges to allow or deny them to users of this new role.
When you have created the new role you can then edit any user account and change their role to the new one. This will take effect the next time that user logs out and back in again.