To start recording press center key or call key.
A small red button shall confirm the recording started.
Any other key will stop recording. Callend key will also leave the app.
On Gerda Os the power key allows you to keep recording in background.
Then you can find your recorded sound as an .ogg file on the root of your sdcard, with the name recorder - XXX.
This app is basically developed by N.Shimizu for Firefox Os