To record your voiceover make sure the Microphone is enabled in your web browser.
Click on the lock icon at the top left next to the search bar
If you see a prompt click Reload to apply the settings.
Select your default microphone from the dropdown list.
Click Start Recording.
Once you're finish, click Stop Recording.
Give your recording a name and click Save.
Your audio file is now ready to be downloaded to be used for your projects.