Have you ever heard of React (JavaScript Library)
i had not heard about it but learned it is a javascript library for building user interfaces
What does it mean to build a user interface?
its like a way the human and computer interacts, like how your screen looks and where you click on pages 
So is JavaScript a computer language for that?
yes its one of the three core technologies along with html and css on the internet 
Which one is the easiest to learn?  I would love to learn one.
HTML
Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript.
Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages. HTML describes the structure of a web page semantically and originally included cues for the appearance of the document.
HTML elements are the building blocks of HTML pages. With
React (JavaScript library)
React (also known as React.js or ReactJS) is a JavaScript library for building user interfaces. It is maintained by Facebook and a community of individual developers and companies.
React can be used as a base in the development of single-page or mobile applications, as it is optimal for fetching rapidly changing data that needs to be recorded. However, fetching data is only the beginning of what happens on a web page, which is why complex React applications usually require the use of additional