New Google Contacts doesn't have the option to copy and past a list of email addresses into a label (groups are now called labels) like the previous version of Contacts.  However, you can import a list of email address into Google Contacts and then rename the label to use in email. 

How to video: 

How to steps:

1. Create a CSV file containing the column label "email" and then listing the email addresses beneath it:
   
   Or use this one importing contacts.csv
2. Save the file somewhere on your computer so you can find it later.
3. Open Google Contacts
4. Click More > Import
   
5. Select your csv file and click Import
   
6. Your contacts will be listed under a new label called Imported on [current date].
   
7. Rename this label by clicking on the pencil.
8. To use this label in email, open your email, refresh the application.
   
9. Compose a message and start typing the name of the label.