You need Google Chrome, FireFox Nightly or Opera (the app should support soon other browsers) + don't forget to set the default input in your OS preferences. If you plugged a guitar in, then press the pulsing button in the middle of the Amp to activate it. Otherwise you can try the amp with the audio player on the left, press play and use the preset menu or the buttons/sliders.
The preamp is close to the one from the famous Marshall JCM 800 guitar amp.
Press play to preview presets
Choose a demo sample:
Use sound wave
DRIVE : distorsion levels
Transfer function and distorded signal example...
toggle / activate the switch or focus the param
up/right to increase value / down/left to decrease value
set to default value
Edit with Keyboard
edit the value directly
rotate upward to increase value / downward to decrease value