You need to unlock your phone to use the navigation buttons that appear at the bottom of the screen.
However, you can also use the Android Wear smartwatch or remote control feature in this app if your phone is paired with Android Wear smartwatch, just touching the play/pause button on your wear device will playback or pause the current track (only for wear devices running android wear 5+. for older versions, click the round button).
Furthermore, notification controls are available so you can control music playback from any screen including the lock screen! This allows you to fully enjoy all the features without unlocking the device every time.