If somebody with a vagina, uterus, and ovaries has sex with somebody with a penis and testes, it’s possible for conception and pregnancy to happen.
When you ovulate, you release an egg into your fallopian tubes. If your egg accepts a sperm, fertilisation happens.
When somebody cums inside of your vagina, the sperm in their cum makes it way towards your uterus. Your immune system kills slow and dying sperm, and your uterus and fallopian tubes direct other sperm towards the egg you released during ovulation. One sperm will be accepted into your egg. Your egg will immediately harden its outer layer after this sperm is let in — to keep other sperm out.
Inside of your egg, the DNA of the egg and the DNA of the sperm join together. This combination of DNA creates a new cell that has its own unique genetics.
After a few days, this new cell starts to divide and multiply. The cell divides into two groups — one group will become a foetus, and the other group will become a placenta. The cells keep dividing and multiplying — forming a zygote. This zygote travels for 3-5 days towards your uterus, where it implants and continues to develop.