After ovulation comes fertilization and then hopefully implantation.
During your monthly cycle you will release an egg which is known as ovulation. The egg is going to be alive for up to 24 hours waiting for a sperm to come along and fertilize it. If the egg is not fertilized it is no longer viable and your monthly cycle will continue and your will get your period about two weeks later ovulation. If the egg is fertilized then the egg is going to implant into the soft lining of the uterus and start to grow and develop into an embryo. Once a fertilized egg has implanted it is not possible for you to ovulate again due to the hormone changes that take place.
It is rare but possible to ovulate more than once during your monthly cycle. If you are trying not to get pregnant there is never a safe time to have unprotected sex.