If you have been invited to join a new organization, you must accept the invite before you can access the new organization's networks or devices. If you have been invited to a new network within an organization you are already a member of, you will automatically be added to that network and it will appear in your list of available networks. If the network is within an organization you are not yet a member of, you will receive an invite to join the new organization.
Upon being invited to a new organization, you will receive a notification with a link to accept the invite. You will also see a small blue dot to the right of your organization switcher near the top of the page. When you open up your organization switcher, you will see a Pending Invite for the organization you were invited to. If you click the organization, you will see an invite acceptance link. Upon clicking Accept, you will now have full permissions within the new organization.
For a walk-through of how to accept network and organization invites, please see the video below: