There are a few different ways that gay couples can use IVF to have a child. One way is for one partner to donate sperm, which is then used to fertilize the other partner's egg. The egg is then implanted into the uterus, and the pregnancy proceeds as normal.
Another way is for one partner to donate sperm and the other partner to carry the pregnancy. In this case, the fertilized egg is implanted into the carrying partner's uterus.
Finally, it's also possible to use donor eggs or sperm. In this case, either donor eggs are fertilized with donor sperm or vice versa. The resulting embryo is then implanted into one of the partners' uteruses.
Whichever method is used, IVF offers gay couples a chance to experience the joys of parenthood together.