Answer: men ejaculate when they have "finished the job" and when they reach climax, but pre-ejaculate (pre-cum) is when they ejaculate earlier than expected maybe because of too much excitement and arousal.
Answer: Well in a male you release semen, which is sperm and liquid that carries sperm. Which then can lead to pregnancy if the sex is unprotected and if you are just ejaculating on your own nothing happens you just clean yourself up. In a woman when you cum it is just liquid, vaginal secretions.
Answer: First if you are asking how to make a boy have an orgasm are you old enough to be having sex? Secondly, by masturbation or sexual intercourse you Stimulate the penis in an up and down direction very rapidly it will send of endorphins and the man will have an orgasm.
Is it possible to pre-ejaculate after you completely ejaculate?
No ... once one ejaculates they cannot pre-ejaculate .
Answer: Yes, its greatest the first time you unleashed it, but it starts to slowly run out the more you kept doing it. This does not mean potency necessarily decreases though. so if you want to keep doing it, even after you have already done it once, then be my guest, keep on doing it.