When he wants to spend a lot of time with you. Also when he calls or texts you at least everyday, presents you to his parents. Its not up to me to tell you if he likes you or not, just believe in him and everything will be fine. :)
It is ok to like a guy after you know he likes you. That is perfectly normal and a part of life.
If you like a guy then get a chance to know him. Find out what he likes and start by building a friendship with him.
If a guy likes you but you don't know him he may look at you or walk by you whenever possible.
Not sure how you expect someone to magically know something.
If he says i like you
This is a tongue twister. And no.
If a guy likes you he will flirt with you but if he doesnt like you then he would act like he hates you.
if he acts like he doesn't
Ask him
Lightly flirt with him. There a probably flirting tips on the internet if you need help with it.
You wait.
nothing! they maybe know that the guy you like likes you back!