I don’t understand how to message users back through the system

Hi, I’m new to this plugin and I’m still trying to figure it out. I see that you can view a user’s activity in the CRM, and you can manually update it. If I add a message, that message does not get sent to the user.

If I create a form on the front end, and a user submits to it, this will generate an email. But after that, how do I reply to them?