Performance mode is the default app mode. This mode is designed for using your tablet/mobile device as an on stage replacement for a song book and bulky ring binder. For most users, this will be your only use for the app.
The main features of the app can be found by swiping the song menu in from the left edge of the screen, the settings menu from the right edge of the screen, the page buttons on the right of the song display and the actionbar. For more information on these, check out the 'Finding your way around the app' section.
If you are using a large tablet/Chromebook, you will likely be able to fit the entire song on to the screen at once. This saves you having to worry about scrolling the page. If, however, you are using a phone or have poorer eyesight, you can change the autoscaling method to best suit your purposes. See the section on 'Scaling the text in a song' for more information.
If you are performing in a venue with a data projector or TV with cast features, you can cast your display to a big screen. You can choose to display lyrics only, or show chords as well. The cast display in Performance mode is set to autoscale full and cannot be customised.