Isn't there a help file to download?
Ok, assuming not, just click the ON button at the top left.
I used it with a microphone in front of a speaker.
You can stick a 1/8"/3.5mm minijack in the microphone jack with a couple of twisted wires and do some playing. It can do A & B channels, so use a stereo jack.
With nothing plugged in, it is pickig up me humming via my laptops microphone, that is displayed on top.
The bottom shows frequency breakdown.