Create a group
Go to Google Contacts.
At the left under "Labels," click Create label.
Type a name, then click OK.
Add or remove contacts from a group
Go to Google Contacts.
Check the boxes next to the contacts you want to add to a group label.
At the top, click Manage labels .
Click the group label you want.
Click Apply.
Add recipients to your email
Click on "Compose"
Click on "To"
Click "My Contacts" (It's on the right side of the second line)
You will see "All Contacts" then under it, a list of your labels (groups)
Click on the Label you want
Click the box next to "Select All," or if you don't want to send it all of them, click on the addresses you want to sent the message to
Finally, click "INSERT" on the bottom right of the page (it's written in white in the blue banner)
The addresses will populate the "To" field and you're good to go.