This app does not really needs instructions since you can’t really mess with it too much.
The main thing is that the interface may seem a bit counter intuitive at first glance: you find the main menu by sliding to the right. The Dashboard is where you see everything happening, the other sections speak by themselves: Subscribe, Publish, Stored Messages and options. To be able to connect and thus use the app, you first have to enter the proper setting. The only setting needed is the broker ip which is 192.168.12.172, the others are either optional or set to what you need by default.