Employers can use the Messaging functionality in K12JobSpot to invite you to view and apply for their vacancies. These invitations are sent through the "Messages" section of the application, so to get started, you will need to select the "Messages" tab in your top navigation bar.
This selection will open the message center where you can select the email in question and view/reply to the invitation.
Want to make sure you can receive invitations? Reference your Resume Visibility Settings (as outlined here) to make sure your information is visible to employers.