If you have not yet created an agency please follow the steps on Creating an Agency. Once you have an agency created, then it is possible to create various roles and permissions for co-workers (someone who works at the agency / should be able to manage all of the accounts in the company(s) under the agency) and send them an invitation to manage the accounts.
Keep in mind that only the owner of the agency can create a new role.
Creating a co-worker permission set
You can follow these steps to create a co-worker role with a specific set of permissions:
Click on the Profile icon in the top right.
Choose the Agencies option.
Select your agency from the dropdown menu.
On the Agency dashboard click to Create Role.
Type in a name for your role.
From the drop-down choose Co-worker role type.
Select the permissions or actions you wish the role to be able to perform and click the Add button.
When you are finished editing your role click the Apply button.
Invite a Co-Worker
When you have a Role that you would like to assign to a person that will be able to manage all of the accounts in the company(s) under the agency can invite them following these steps:
From the Agency dashboard click to Invite Co-Worker.
Fill in the user's name (it will be used in the invitation email as a greeting).
Fill in the user's email (this email would become their login with which they will be able to manage the accounts).
Choose the role which you would like to assign to the person. (the user's permissions will be restricted depending on the permission set of that role.) Note that you can choose only co-worker roles!
If you choose the Auto accept invite option, the user will not be able to decline the invitation
Click Send Invite for the user to be sent an invitation email.