We all know that one individual, may it be that girl that sits in the back of all of your classes or that guy that is always in Starbucks. You know their name, but you've never interacted with them personally.
They're almost always alone. If they are with other people, it's usually the same group of 3 (maybe 4). They usually have their headphones in and constantly look down when they're walking. They probably just smile or nod when you greet them in passing. They usually avoid conversation.
You may mistake this person for being rude or mean or even "uppity". This usually isn't actually the case. This individual is probably just incredibly introverted.
Introverts make great friends if you do everything right.
The first thing that you need to keep in mind whilst attempting to befriend an introvert is that they will never initiate conversation. That part is up to you. At first, it may seem a little awkward as they'll probably just respond with the bare minimum. This isn't because they don't like you or don't want to talk to you, it's because they just don't have the same socially interactive capabilities as most people.
The next thing to keep in mind is that it may take a while for an introverted person to break out of their shell and actually engage in meaningful conversation. It also may take a while before that person is comfortable looking at you and making eye contact when speaking. You just have to be incredibly patient with them.
A last thing to know is that they will (eventually) open up. Introverts, when comfortable, can be some of the loudest, most ridiculous people you'll ever meet. It will all be worth it in the end, you just have to be patient.