I will give you a woman's point of view. Get to know the girl and when you are sure by her gestures and words that she feels the same about you then you can express your admiration or love. Make sure that you see her face to face, not just via msn/txt. otherwise you won't be able to see her feelings for you in her eyes. You could express your love by sending her flowers or a nice card/email/poem etc if you are too shy to tell her in words at first.