Jquery is a Javascript file that you add into your javascript folder, this file has a lot of premade functions that shortens the time typing Javascript. It allows you access different CSS Selectors and traverse the DOM with far less lines needed. It can do everything that Vanilla Javascript can do just in a shorter amount of time. As Jquery is a Javascript file it should be linked at the bottom of your Index page. The reason for this is that when the browser reads a Javascript page it stops reading all other documents, this slows down the rendering of the page. So placing the Jquery file at the bottom of the body is the preferred practice.
Pair Programming is a process that involves two different people: The Driver and Navigator. The Driver physically codes while the Navigator directs the Driver. This helps to speed up the thought process behind coding as well as lower the chance for errors. If they are both stuck you automatically have 2 people familiar with the code to research and find the solution. It also helps for learning, by Pair Programming you can gain experience in how the other person thinks about and writes code. This helps to speed up the coding process and delivers a higher quality code than each person working seperately.