The simplest action a user can do with our app is a tap. Almost all applications aimed at engagement usually have an action as simple as this. It is common to see it as a heart or a thumbs up:

Its functionality is highly effective. Thanks to a small contribution of our user, it allows us to offer better results in the future, based on your preferences. In addition, it allows us to know what contents of our application are really interesting for the majority of our users.