Castmill allows you to login using different mechanisms, you can create a custom Castmill account, or if you prefer you can login using your existing Google, Facebook or LinkedIn accounts. Access the castmill app by pointing your browser to https://app.castmill.com.
The login dialog
As soon as you login, you will get to the main dashboard. From this dashboard you have access to everything you need in order to operate your players and program the content that you want to display on them.
As you can see, the "Players" tab is preselected, and as expected there are no players in the list.
In Castmill a Player and a Display are often interchangeable. In reality, a player is usually a piece of hardware connected to a display, but sometimes the display has a built in player.