Buttons are the execution of any action. For example, you can create buttons to execute: Copy to clipboard, Send an email, Open a link, Link to page and others.
For example, you want to add a button that will send emails. To do this, select the type of Action - Run Operation, and then configure the action to send an email (example below: using Sendgrid to do this). For more details about how to set up Actions, see here.
More information about Actions.