Before using your Microphone for Voice Calls, and your Camera for Video Calls, you may have to grant permission for apps to access your Microphone and Camera.
To get started, go into Windows Settings > Privacy > Microphone AND
Windows Settings > Privacy > Camera.
You'll see two toggles under the "Allow apps to access your camera/microphone," turn both of these to "On".
You may need to restart the browser or program that is requesting either camera or microphone.