Outside of messaging for an appointment, click the Engage tab on your Squire page.

Click the Create Campaign option and then select "Quick Update" as your campaign type to create a new message. You'll be able to draft your subject and message, customize it with your brand colors and even add your logo and a background image. You'll be able to add links and stylize your message and review before sending.

You can then select how to send messages and what groups you would like to send to. Click Review and Send when finished.