"Message" in Spyglass are three things: you can do something to another person (e.g. give a hug, a kiss, or spank someone, etc.) or just say something, do it secretly so only your "victim" can see the message, or you can let someone else do or say something. Additionally to sending the textual message, the Spyglass will also play a sound and animate your avatar if appropriate.
Click the button to send a secret message, the button to do or say something in local chat that everyone near you can see, or click the button to do or say something as someone else.
You will see a menu from which you can pick the message you want to send.
The messages in Spyglass are fully customizable. To edit the messages you can send, open the Spyglass's inventory (right click the HUD and choose "Edit" from the wheel menu, then go to the "Content" tab. Locate the "_Message" notecard and open it. You will find an instruction inside the notecard how to edit it. Once you are done, click "Save" and your new or modified messages are ready to use.