The buttons for call answer/end, volume, and mute are on the inline remote of your headset.

Call answer/end:
To answer an incoming call or end a current call, press the button with the icon of a phone handset.
The call answer/end button won't start a new call — you do this in your conferencing or softphone application controls.

Volume:
To turn the volume up, press the top of the volume button, and the bottom to turn the volume down.
You'll hear a high-pitched tone when you press volume up, and a lower-pitched tone for volume down.

Mute:
Press the mute button to mute the microphone. Press it again to disable mute. The mute button turns red when mute is active.
NOTE: Button functionality may vary depending on your chat or softphone application.