The fusion of male gamete i.e. sperm and female gamete i.e. ovum is known as fertilization.
When the egg gets fertilized:
After the egg drops from the ovary, it travels through the fallopian tube, where there is about a twenty-four-hour window till then it can be fertilized.
If everything is under favorable conditions, then the sperm meets the egg in the fallopian tube and the two half-genomes fuse.
This leads to the formation of a complete set of genes containing all of the DNA that is necessary to make a new human being.
Thus, the egg gets fertilized.
The fertilized egg then moves down the fallopian tube towards the uterus.
In the uterus, the egg gets attached to the uterine lining.
Once sperm has fertilized the egg, the blastocyst multiplies its cells & gets implanted on the uterus wall.