Pick a note and let it sound while you play scales, long tones or a tune against it. Add the fifth or the octave, or hold a whole chord. Against a drone, a note that's out of tune is easy to hear.
What sounds can it play?
Strings, violin, cello, bass, organ or a plain sine wave.
Can it hold a chord?
Yes. Major, minor, sevenths, sus chords, or just the root and fifth.
How do I practice with a drone?
Play a scale slowly over the drone's note and listen for each note to settle against it. When a note is out of tune you hear a beating, wavering sound.
Can I change notes while it plays?
Yes. Tap another note on the circle and the drone moves to it without stopping.