The buttons have multiple functions, which are described in full in the Online Owner’s Guide for the Bose Sport Open Earbuds.
Right earbud button:
Single-press to turn on.
Press and hold to turn off.
When on and in audio playback mode, use the right earbud button to control content: play/pause (single press), skip forward (double press), and track backward (triple press).
When there is an incoming call, single-press the right earbud button to answer the call or double-press to reject the call. During an active call, single-press the button to end the call.
Left earbud button:
Single-press to initiate the earbuds’ shortcut function, if enabled. Set the shortcut function in the Bose Music app.
Press and hold to access Siri on an iOS device or Google Assistant on an Android device.