First of all, Mr. Kumarguptadeepak, the spelling is "sperm" and not "sprem".
The sperm swims actively from the female vagina to the Fallopian Tube. If there is an ovum in the Fallopian Tube it gets fertilized by a single sperm. The head of the sperm (the nucleus) fuses with the ovum to make it fertilized. This is the process of Fertilization.