Question

how male game fusion with female game ?explain in detail?

Answer 1

During copulation,male releases million of sperms by the process of spermatogenesis and enter into the uterus through cervix and vagina ... and then fusion take place bet the ovum and the sperm

Answer 2

Because that is the purpose of gametes. They're essentially haploid cells which have to fuse to form a zygote so that the species is continued. Gametes are reproductive cells.

Since they both carry only half a set of chromosomes (haploid) from either parents they have to fuse in order to get a diploid zygote which contains the full set of chromosomes. That in turn develops into a new form of the organism. Gametes cannot develop on their own (I've heard of that in plants but you'll have to consult a botanist on that).