Submit Action
A submit action fires a webhook to the developer’s web-service with the current state of the card, including the values entered into any interactive components, so that the developer can trigger side-effects and/or return a new set of components to update the card state.
More on how this works is in the submit flow documentation through this link.
Input Components
If there are input elements present within the card, then a submit action from a button will submit the entire form.
action: { type: "submit" }