I really really worry that you are prepared to jump in when you so far know so little about it (and so early in the relationship). But here are some answers to your questions:
after i have sex do i have to go to the doctors?
No, not unless you are pregnant or have picked up a sexually transmitted disease. However, women, especially if sexually active, should get a regular Pap smear done to guard against cervical cancer.
i'm afraid of my hymen breaking in front of him, is there a way i can tell if it's broken or not? and could i break it myself?
If you use tampons your hymen has probably already broken. If it is intact, it will be broken by his penis. There will be some blood. A doctor can tell you if the hymen is there; or you can check yourself with a mirror.
it's my first time and not his, how DO i have sex?
There should be a considerable amount of making out, feeling, etc first, and you need to be in the mood and ready, or you won't be lubricated enough. This doesn't matter so much to guys, who are ready most of the time, so you need to be prepared to be assertive. Don't assume he is a great lover. Make sure he uses a condom. If he is not prepared to use one, there should be no sex.
There are a lot of different positions, but missionary is a good start: the girl lies on her back with legs apart, the guy lies on top, supporting his weight on his elbows so he doesn't squeeze the life out of her, his legs between hers. You can guide his penis in the right hole, since many guys have trouble finding it.
what am i suppose to do to give him pleasure?
He'll move in and out as gives him pleasure, and you are supposed to enjoy it.
besides getting pregnant what do i have to worry about?
Sexually Transimitted Diseases for a start. Some of them are very common. A condom is essential to provide some protection; however it gives only partial protection against herpes and genital warts.
You should also be careful of your reputation. Is the guy going to brag to his mates?
how would i know that he likes it while i'm giving it to him?
He will, don't worry.
what can i do to give him pleasure?
You asked that before.
after i have sex do i have to go on birth control?
Yikes! Birth control (contraception) is something you arrange BEFORE sex. Condoms (which should always be used to provide some protection against STDs) are not bad for birth control provided they don't break or come off (it's important that he pull out soon after ejaculation, before he starts going soft). The condom can easily break or come off if used by the inexperienced, so it's a very good idea if you are on oral contraceptives as well. These need a doctor's prescription.
You may have been thinking of the "morning-after pill", which is to be taken after sex. It needs to be taken within 48 hours. It has strong side-effects, and is only suitable for emergencies (such as if a condom breaks), not for regular contraception.
and after i have sex, it's done, no one have to know and i don't have to see anyone?
Yes, if you are not pregnant, didn't catch an STD, no-one heard you and your bf didn't tell everyone.