Where did it come from? Why is it here?

Nobody knows for sure where the origins of April Fool's Day came from. However, most will speculate that it started in the 1500's. This is because there was a transition to the new Gregorian calendar that we know now.

The old calendar had the new year begin at the end of March as opposed to now when it's in January.

People would try to trick other people into believing that New Year's Day was April 1st. Those that believed were "April Fool's".

Another theory is that because of the unpredictable spring weather that people would often be tricked into thinking it was nice outside.