1) Precum is released when he gets aroused. So if he has an erection, it most likely have precum dripping from it.
It is the same fluid making up semen but without the sperm added. It is used to lubricate him and clear the way in the unary tract for sperm to pass through safely. It gets the pH right for the sperm to survive the trip by cleaning the remnants from urine.
2) Precum does not have to contain sperm. The semen there are normally what is left over from previous ejaculations for example masturbation. If he urinated between the last ejaculation and sex, there should be very very little sperm left. It is not as if sperm are escaping from his reproductive tract and gathering waiting for him to get aroused. There might be medical reasons for sperm leaking before ejaculation but that is the exception.
3) The outside is called the vulva. The vagina is the tube from the uterus/cervix to where it mouths out in the vulva (where the hymen used to be). Precum have very very little chance of getting you pregnant if it lands on the vulva. Something needs to take it inside the vagina and drop it close to the cervix for it to have any chance.
