If you want to use Organizational Roles, you first need to add users to your organization. The head of the organization is the only account that can add admins.
Logged in as the head admin, find Manage Users in the drop-down from the upper left menu.
Here, you can enter the email of the new user and send them an invitation.
They'll get an email with a prompt to accept the invitation. If they don't have an account already, they'll be prompted to create an account when they click on the invitation. If they do have an account with that email address, they will automatically be added.
Once the new user has accepted the invitation, you'll be able to share your meetings with them.
You can also remove admins from your organization to make space for others.