If you want to make an email group in Gmail, first get to Google Contacts, then hit Create label on the left, and give your group a name. Afterward, select the contacts you wish to add, tap the Manage labels button at the top, choose the label you created, and press Apply. At the moment of sending out an email, simply enter the label name in the "To" field of a new email, and Gmail will fetch all the contacts in the group for you.