Google Hangouts is being deprecated over 2018 as Google updates to Google Hangouts Meet. However, you can still record classic Hangouts via Hangouts on Air/Youtube live.
Before you begin using Hangouts on Air, you will need to verify your YouTube account. Account verification takes 24 hours.
Under Basic Info, create a Title, and pick a Start Time.
Be sure that the Type option is set to Quick (using Google Hangouts on Air).
In the privacy settings drop down menu on the right, select Public, Unlisted, or Private.
An unlisted event is viewable to anyone with a link to the event, while a private event is viewable only by people you share the event with.
Click the Go Live Now or Create Event button when you are ready to start or save your event.
If you need to share a future Hangout’s details with participants, click the Start Hangout on Air button and add participants. You can then leave the Hangout and come back to it at its scheduled start time.
NOTE: Your recorded video will upload to your YouTube channel once you leave the Hangout on Air.