In order to add users to your account (we call them "Agents"), you'll need to invite them first. Once a user is invited, they will receive an email which invites them to join your organization.
Navigate to the agents area in Keeping's settings. Once there, click on the "Invite Team Member" button in the upper right.
Enter in the email address for your agent, along with their first and last names. You can also adjust their role (Admin or Agent), and which mailboxes they will have access to once they join. Click "Send Invitation" once you are done.