Start with the volume low
Left and right send the tone to the selected audio channel. Stereo sends it to both. The volume control changes the generated signal, not your operating-system volume.
A worked example
Left sends a signal only to the left channel; the right channel contains silence. Each tone stops automatically as well as when you press Stop.
Before you use the result
Mono settings, Bluetooth profiles, cables and output selection can combine or swap channels. The page generates a signal; you decide what you hear. No microphone access is requested.