From the sidebar:
Click on “Message Templates” on the left sidebar
Click “Add New Template”
Create your template, filling in Text (SMS), Email and/or Voice content.
Click “Save.”
Your template will be available when you compose an individual message or a group message (campaign) and will be private unless you choose to share it with your team.
You can also create message templates prior to sending a message by clicking "Save As Message Template" while composing an individual message or a group message (campaign).