Climaxes, orgasms, 'coming' - happens as a result of having sex. Both boys and girls have them although they are different in nature for each. Not all sex has to end with having a climax or orgasm. Sometimes too much emphasis is put on it, and this causes anxiety and worry when it does not happen.
Sometimes it is just nice to have a bit of sex and not actually have an orgasm. Boys' orgasms tend to build steadily up to a peak during sex. The actual feeling of 'sex' tends to be concentrated in and around the penis. From starting to have sex (whether masturbating, or having sexual intercourse) to reaching a climax may take less than a minute or 10 - 30 mins or more, or even not happen. When a boy has an orgasm, normally he spurts his sperm out of the end of his penis or ejaculates (though this may not always happen - it is sometimes a dribble and sometimes does not happen at all). Girls orgasms tend to be slower in building up, and involve a more general feeling of sexiness throughout their body. Their climax tends to last longer, and feel more generalised than boy's climax and may vary considerably in intenseness. During the female orgasm, the vagina contracts.