A useful way to think about apps is through the way users interact with them. Two very basic levels of interaction are viewing & editing data.
But very often, apps need to be able to perform Actions.
For example, in this app, we have a button which when clicked will take people to a website. This is because the button has the action Open Link enabled.
You may not have thought of it this way before, but opening a Form is a type of action. If you look closely in the Form Button's configuration, you will see the action 'Show Form' enabled.