How can you flirt with someone?

How can you flirt with a guy not being noticed by other people? And how do you know if someone likes you and wants to have a relationship with you without telling you?How can you flirt with someone?
Things like passing a note if your in middle school or high school. And lighting touching his hand or something like it's an ';accident';. Those are things that other people might not notice. Also laughing at his jokes. Guys love when you laugh at their jokes. If a guy calls you or talks to you a lot, or walks you to class, sits with you at lunch things like that are good signs that he likes you. If he wants to hang out with you a lot, it's a good sign that he wants to be in a relationship with you.