How to add libraries in visual studio : <p>I will be going to university next year and I am trying to learn myself how to program in C#.
I started with a new project on visual studio, and I pasted the program below from my textbook in a empty project.
As you can see, in the first 2 sentences, there are a couple of libraries used that visual studio doesn't recognize. What am I doing wrong here?</p>

<p>complete beginner btw.</p>

<p><a href="https://i.stack.imgur.com/KZ8mE.png" rel="nofollow noreferrer">the pasted program from my textbook</a></p>
