Open the Messaging app and tap the ‘+’ symbol on the top row of the screen. This opens the New Hangout screen, which has a line labelled ‘Type a name, email, number or circle’. Here you can start typing the names of the contacts you wish to contact.
Note that on new devices the SMS app has been combined with Google Hangouts. Therefore, if you specifically want to send a group text message, you need to type the full contact name so that you are offered the full set of contact options for that person. However, by messaging people via Google Hangouts, you will avoid charges.