To use just:play you need to connect to a Channel using the Just Control application.
Go to your Applications folder and open the folder Just Playout.
Open Just Control. The Login window shows up.
Enter the username and password. Consult your system administrator if you don’t know these credentials.
Optional: select a Multi-viewer layout. It may be the case that this menu only allows you to select the Default layout.
Click the Login button to start Just Control. The Multi-viewer is shown with all channels available for the selected user.
Click on the button in the middle (marked in red in this figure) of the channel you would like to work with.
The corresponding channel will be opened and the just:play interface shows up. As you can see, a tab bar is now shown, allowing you to switch back to the Multi-viewer, or closing the previously opened just:play user interface. Note that when closing the user interface, the playout will continue to run, unless Just Out and/or Just Connect are terminated as well.