You know if a boy likes you, if he:
Stares or smiles
Will try to sit next to you
Tries to make a small quick conversation with you
(If has long hair) Flips his hair around you
Is asking different questions about you
Asks for your number
etc., these are only a few. If your guy does some of these things he must like you!
Chat with our AI personalities
Yes, you can express your feelings to a boy by telling him directly that you like him. Be sincere, confident, and considerate of his feelings in your approach. It's important to be open to accepting his response, whether it's positive or negative.
It depends how close your are to them because if you hardly know them then its kind of strange. But if you are close then you could just come out and ask it.