The Google Messaging app should already be installed on your watch. You should be able to send and receive texts from Google messages on the watch. You will have to make it your default messaging app on the watch. If you are having difficulties with texts being sent or received on the watch, you need to contact your carrier, as they may not have provisioned the watch properly for messaging when disconnected from your phone. You should always be able to send/receive texts with the watch connected to the phone, even if connected remotely.
