How do I add new Users/Administrators to my Dashboard account?

To add a new User to your Dashboard account (to your "Organization"!), start by logging in to the Dashboard.

Go to the "Settings" menu (see the main menu on the left.)
From here, you will navigate to the "Users" tab
Click the orange "Invite User +" button and follow the instructions.
Make sure to assign the appropriate Permission Level to the new User (don't worry - you can change it later if necessary).
When you're all set, click Send Invitation, and an email will be sent to the invitee with a link for them to setup their password.