I am currently a mixture of introvertedness and extravertedness; at least I am that on the outside.
About two years ago, I was more of an introvert. I had to main friends at highschool and knew a few other people. I never really talked to anyone unless they talked to me first.
Then after highschool finished, I got myself a job as a cashier in a supermarket. Since I wanted to do the best job I could (so I did not get fired or whatever) so I had to learn how to make a conversation with a person I knew absolutely nothing about. Now-a-days I just have a routine that I have developped but when I started, I almost found that I could do it naturally.
So then I started college a few months later. The first few days were scary, I knew basically no one. One day a girl sat next to me and we became friends. Since then I have made many friends and even introduced a fair few people. I am starting to understand the first few steps to approaching someone without knowing them but I sometimes cannot bring myself to do it.
So if you want to be friends with someone, there is no harm in approaching them and getting to know them

, the worst that can happen is that they have no interest in you.
I am still a bit confused about myself, I am equally happy with doing things with others as I am doing things alone. Really I am not sure which one I am. Those who have known we for 2+ years would say I am an introvert. Those who have known me for less than two years would think I was an extrovert. I was not sure which one I want to be the most. I think I am still afraid of what people think of me if I say or do something odd.
One of my really shy friends does best when she is only with one other person. When we are in a group of 5, 3-4 of us would do the talking and she would do the listening. I feel as if I need to include her. However when it is just me and her we can have some very nice conversations. Maybe you are one of these people?