The organ of maximum sexual pleasure in males is the penis, particularly the head of the penis. The organ of maximum sexual pleasure in females is not the vagina but the clitoris, the small hooded bump above the urinary opening. Male orgasm involves ejaculation of semen into the vagina during rhythmic contractions over about 5 to 20 seconds. Female orgasm involves the rhythmic contractions of the vagina for 5 - 20 seconds. Female orgasm is not required in order for conception to occur.
Oral sex involves the contact between the mouth of one person and the genitals of another person.
It's considered unsafe because it is through these fluids that AIDS and other STD's are passed from one person to another. It is also through contact between semen and vaginal fluids that a female can get pregnant. The egg is many times larger than each sperm. Once safely implanted, the fertilized egg begins to grow. Pregnancy has begun.