Message extension is a new ad extension which will appear along with search ad. Message extension will allow user to send you message to start conversation. This is another great option for people to reach you. With message people can ask for a quote, book an appointment, ask for information they need and more.
Your business should have a mobile number and your mobile phone should be able to receive and send text messages.
When someone click on message icon on your ad, sms app will open with an auto populated message created by you in their mobile phones. Click on message icon is charged as a click similar as user is charged when they click on ad to see website.