An orgasm might happen spontaneously when you make love, but often this is not the case. Many girls first have to find out how to come on their own before they can climax with a guy. If you want to know how to climax you have to find out what gets you excited. So you have to take some action:
Try to masturbate. That way you’ll learn to know your own body and how it responds to sexual stimulation.
Getting an orgasm is not achieved by pushing the right button. In order to climax sex needs to fill your mind. So look for stories that excite you, erotic pictures and movies and develop sexual fantasies.
Once you get very excited you must keep stimulating yourself. If you stop too soon you will not get past the plateauphase.
Don’t think about wanting to orgasm, but be oriented towards things that excite you. If your excitement keeps increasing you may come to orgasm.
Try a vibrator. Many girls who are unable to orgasm using their fingers, can climax using a vibrator to stimulate their clitoris.