Step 1: Set up the Event and related Session in Salesforce. On the session, in the Sessions <> Organizations related list, click on New Session <> Organizations.
Step 2: The session name will automatically populate for you. To select an organization, click on the magnifying glass icon, type in the name of the organization, click go and then click on the name in the search results.
Step 3: You should now see the organization name in the organization field. If you only need to associate one organization with the session, click on Save. If you need to associate multiple organizations, click on Save & New and repeat these three steps.