Depending on the kind of guy he is, he might tell you the moment he realises he fancies you, a day later, a week later, months later or even infinite later, in other words he might never tell you.
Simply smile and let him know that it makes you happy that he likes you.
If you like him to you should let him know how you feel and take it from there
Just ask him. He will let you know with his mouth or his body language.
let her come to you
I let you know after I find out.
Keep this to yourself do not let him know it is your greatest secret!
It mean he is trying to let you know he likes you by complimenting you.
He teases you.
First establish that she likes you then let her know that you like her ask her out, take her to a movie be a gentlemen. After that things will just flow.
If he likes you then you already have the hard part over with, just talk to him more and let him know you feel the same way. Then let the rest take its own course... if he doesn't try to find the courage to ask him out yourself
Let him down gently and let him know you are not interested.
Depends how old he is... if he is always looking at you and you have to let him know if you like him or not.