You can invite Users by Podio or by email. (Read How to add New Users >>)
If you invite them by Podio, inside Podio, they will get a message from the Account Owner/ Administrative User who has created the invite.
There is a link in the Podio chat message where they can enter directly into your smrtPhone account. It's very important that they click the link within the Podio chat (rather than go to the smrtPhone website) because that link contains specific information that makes the sign-up / login easier.
Once they click the link, they will see a screen within smrtPhone that prompts them to Accept Invitation.
Once they accept, they will now be in your smrtPhone account and users with granted permissions will be able to see and manage them from the User section of the Admin Dashboard.