Answer 1

jQuery is a JavaScript library designed to simplify HTML DOM tree traversal and manipulation, as well as event handling, CSS animation, and Ajax. It is free, open-source software using the permissive MIT License.

Answer 2

For writing queries in JavaScript

Answer 3

It is a javascript library that can be used to make your life easier because it is easy to understand and very efficient. Instead of writing down 20 lines in javascript, you need one in Jquery for the same function. Start learning it, good choise if you want to start with your own website or sth like this

Answer 4

I hope, this help you:
https://www.sololearn.com/learn/jQuery/2782/