There are two methods to start the player: via MyTunify or via the Tunify Player app. How you start Tunify depends on the device you are using.
Are you using a computer or laptop?
Log into MyTunify
Go to "Dashboard" in the left-hand column
Click on "Start player".
And play!
Are you using a smartphone or tablet?
Go to the App Store (iOS) or Play Store (Android)
Search for "Tunify Player”
Download the Tunify Player app
Open the app
Log in with a player code (how does it work?)
And then play!