The doorbell that reacts
A doorbell does nothing until someone presses it, then it rings. Event-driven programs wait the same way — a click, a key, or a tap is the press that makes the code spring into action.
When this happens, do that
An event is something that happens that a program can notice — a key press, a mouse click, or a sprite being touched. Event blocks say 'when this happens, run these steps.' They let a program wait and react instead of only running top to bottom.
'When… ' starts the action
A block like 'when the green flag is clicked' or 'when space key pressed' is a hat block: everything under it runs the moment that event happens.
'When space key pressed → make the cat jump' — pressing space triggers the jump, again and again.