The Video Preview window appears after you click on the link to join the room. Adjust your camera input settings by clicking Settings in the navigation sidebar > Video > choose the desired camera input from the Camera drop-down menu.
Select Call me at and enter or select a phone number, including the area code that you want Webex to call you at. After you click Join Meeting, answer the call when your phone rings and you will be able to speak in the meeting through your phone.
After altering your microphone/camera choice, you may click on Start/Join Meeting.
Click on the caret in the Start/Stop Video button to alter Camera Settings.
Selecting Use computer for audio will connect you using your computer’s microphone and speakers. You can change the input/output devices by navigating to Audio > Speaker, Microphone and Camera.