I got this question from a customer just getting acquainted with email in general and Gmail in particular. Consequently, I put together this quick video showing how to setup email groups and use them to send emails in Gmail.
Here's some "How-to" links from Google as well:
- How to create a group: https://support.google.com/mail/answer/30970
- How to send to a group: https://support.google.com/mail/answer/30973?hl=en