Most of our behavior is taught/learned and can relate to our dispositions/feelings too and what mix we give to our emotions and thoughts to create our actions.

Long story, short; you have not had much practice interacting with others so you are awkward with it; parents can be too busy or not know themselves how to interact well with others, how to teach it, or even just know they need to teach it so we have the added burden of having to figure out how to learn on our own. Having to learn on our own can be lonely in itself but can be made even more difficult by our emotions/fears.

If I were you, I'd watch people you admire for a bit and see what they do and then do an experiment where you "copy" what they do. If you would like to try something, you let others who are doing it know. Sure you may be bad at it at first but everyone is until they learn. Other kids our age are not that much more experienced than we are, some might have more social natures so it's not as hard to approach another but the amount of experience can not be that much greater. Too, there are other kids out there like ourselves, we're not the only "shy" people. Look and identify the others that are hanging out. Getting to know another "wall flower" and then deciding to try stuff together can be helpful. Join a club and just sit through a couple meetings until you get more comfortable about how it "works" and then you can add a comment or two to the discussion, kind of like a regular class but the club will be something that interests you or that you know you know a bit about so will help you be a bit braver.

Make a plan of what you wish you knew how to do and ways to learn it. I was afraid of public speaking so took classes in it and deliberately got included in panel discussions and as an officer of a club, etc. Go toward what frightens you instead of shying away. It's like dreams, you have to confront the monster, not run from him.