Verj.io apps are event-driven. These events run either automatically when your application executes, e.g. a Before Form event will fire before your application has rendered to the screen, or in direct response to a user action, e.g. someone clicking a button will trigger its On Click event.
You control application behaviour by associating scripts with events, e.g. on a Before Form event you may decide to hide or show certain page elements depending on who the user is.