I’m a freshman in high school, and there is a Korean transfer student who is a junior. I’ve been meaning to talk to him for a while, but i’m terribly shy, so I ended up writing a note that basically said that he seems cool and that I would like to talk to him, but I’m shy, so don’t bring it upon yourself to talk to me; I’ll have to find my courage.
I somehow ended up with his number and we talked that afternoon. That was two days ago and I want to text him but I’m: 1) worried I might bother him ,2) really fricking shy, and 3) I’M REALLY WORRIED THAT I MIGHT BOTHER HIM. Not to mention I’m kinda too shy to actually talk to him at school, so it’s more like whenever I pass him in the hall, I smile and wave awkwardly. I need all kinds of help.
LemonVibe 
This is some of the hardest advice to take as a shy person, I know, I’ve been there. And I wish somebody told me this when I was agonizing over the people I was afraid to talk to.
Go up to this person, greet them by name. Ask them how they are doing, and ask them something semi personal that requires more than a yes/no answer. What they did over the weekend. What they do for an upcoming holiday. Even talk about the weather and the change in seasons. Then have a conversation for a couple of minutes. That is it.
You aren’t pushing for anything. You aren’t building this up in your head. You’re asking questions that you should be genuinely interested in and connecting with another (presumably) interesting person.
That’s why it works. If you take away any motive other than having a conversation and learning about someone you can talk to ANYONE. If they don’t talk much or connect with you, nothing lost either. In fact, if someone is bothered by you doing this, it’ll be clear. But if someone is a dick while you’re doing this, you really don’t need to be friends with them.
Yeah, it’s shitty advice telling someone who is shy to just do it. But what I’m really saying is lower the importance of the conversation. By a lot. Makes it easier.
I know it may be tough for you, but I’d agree with the comment above. It may be nerve-wracking, but the best thing you can do is wrack up some courage and talk to him.
You have his number, which means he, more likely than not, is interested. In which case, it’s possible that he likes you back. If you’re uncomfortable talking to him in person, then just send texts to him. Keep your conversations light. When you feel you’ve gotten to know him enough, walk up to him in school. I know it sounds tough, but it’s probably the best way to get over your nerves.
As someone who grew up incredibly shy, I know its hard but the first two commenters are 100% correct. Stop worrying about being a bother and just make casual conversation. I guarantee you that you are not nearly as annoying to other people as you think you are.
I was so shy I barely talked to anyone in high school, I always felt like I was a bother and I still have to push myself to start conversations or text people first but as Ive gotten older Ive learned that my silence often got misinterpreted as me being stuck up or snobbish— because other people worry just as much as you do about being a bother and for the most part everyone enjoys light friendly conversation.
You got this, He already gave you his number! Thats big! Just make small talk and see where it goes.