Anyone can tell me what does an event do ?

Answer 1

Events in general u can say a phenomenon to be occured, and by that phenomenon some thing would change..
So when you click on a button, something should happen, right?
So the "click" is the type of event which may occur.. and due to clicking on it, some things may change..
So javascript provides you eventhandlers, by which you can target that click event and then it lets you decide, to do whatever functionality you want to implement on clicking that button..
So their are many such events, as click, blur, focus, hover, keyup, keydown and many more..
so each event has it's own specificity of occurrence, u can read about all those events here : https://www.w3schools.com/jsref/dom_obj_event.asp

Answer 2

https://developer.mozilla.org/en-US/docs/Web/Events

Answer 3

Thank you