How do I overcome my social anxieties?

I need help becoming more social. I am thirteen years old and am very shy. Usually I sit in my room all day, and only come out only when necessary. I don’t have any friends and can’t relate to any of my peers because of the way I think.
I never understood political correctness and how it works. I don’t know what is and isn’t socially acceptable. I don’t know how to start a conversation. I seem to make people angry when I speak to them. I never understood social behaviors.
I can barely order food at a restaurant, I can’t go up to the counter to ask for condiments, ask questions during a test, ask for anything from my teachers, ask for directions, ask for instructions, or talk to new people. I also have a hard time going to social events like school dances, assemblies, ect. I’d feel like I got the time wrong or something.
I get nauseated and I feel like I will vomit.
I take negative comments to the heart and they will effect me for the longest time, no matter how small the problem.

I need help overcoming this anxiety. Any comments will be stored in my brain for further use on my lifelong quest for knowledge.