When some one put his sperm in a girl from back side. What happened? Is the girl get pregnant.

Are you serious? No... obviously NO!

Your question isn't clear...

When you say from the back side, do you mean anal sex? Do you mean vaginal sex from behind?

If it's anal sex then obviously there can't be pregnancy. If it's vaginal sex from behind then it works the same as any other sex and there is a possibility of pregnancy.