After first install, you will see the following page, you can start adding files and notes by the "+" button, after that, you can tap on the files to go to the music page. A example file with Mozart Sonata is included at first install.
Before start playing, you can check a few settings and change them as needed, tap the gear icon to open the preference page
Set "Wait for correct notes while playing", if you want the App to wait for each note/chord to be played correctly before play the next one.
In the Music Page, first set up the MIDI device by tap "MIDI setup" (use a MIDI/usb cable to connect your MIDI keyboard to your android device) If your MIDI keyboard doesn't show up, there might be some settings in android you need to change. Please check internet for the details. If your MIDI keyboard shows up, tap on it and tap connect. After successfully connected, the device name will be shown next to the "MIDI setup" button.
After MIDI is setup, you can adjus the tempo. and use the forward/backward to adjust where to start playing. Then tap the play/stop to start/stop playing. During the play, the next note to play is highlighted in red, if you play the correct note, it will change to green color. wrong note will be marked as red color.