Here are so many stories about how 1st April came to be celebrated as April Fool's Day but the most wide spread origin is about the calendar . In the year 1582, Pope Gregory XIII introduced a new calendar.
This calendar started the new year on 1st January but back then info took time to spread as there was no internet or phone back then so many people didn't know about the change in calendar and many who knew about the calendar refused to accept the calendar. These people continue to celebrate new year day on 1st April. The people who had accepted the calendar start making fun of these non believer, they would lead them to believe in things that did not exist or even send them on fool's errands, errands that didn't exist.
This harassment evolved to a tradition of playing pranks on 1 April, this then spread to other countries. However April fools has already established in England which didn't switch calendars till 1752 also people were started engaging pranks and lightheartedness around this time of year long before French switched their calendar system such as in case of ancient roman festival o hilarya.
Modern celebrations of April fools have slightly different traditions depending in which country you are in but they all has a similar theme of pranking or humiliating individuals. in France they try to tape an image of fish to your back without your noticing, in Portugal they throw flour at you. and in England you're are only suppose to pull jokes until noon if you pull jokes after noon then you were called April fools . In US in Britain popular media outlets and companies have also been involved in the fun. In 1996 Taco bell announced that it has purchased the liberty bell from the city of Philadelphia and was going to rename at Otago liberty bell in 1992 NPR claimed that Richard Nixon will be running again for president, British publication the guardian famously pranked the public in 1977 that when they said there were simi column shaped island in Indian ocean has been discovered this hoax is credited for launching the trend of April fools day pranks by British tabloids.
Eventually the new calendar was accepted worldwide but the pranks stayed on. parents, friends, relatives, siblings often play tricks on their loved ones on 1 April all the pranks are harmless fun and not to hurt anyone. they usually end with pranksters shouting April fool and peels of laughter from everywhere. So pranking is a prank of celebration.