April 1st is called April Fool's Day in the English-speaking world. It is a day people when people traditionally play jokes. There are often false stories in the newspapers and on the television and radio.
In most countries April fool's jokes usually happen before midday. In France, for example, you have 'April Fish'. Children try to secretly pin paper fish on to each other.
Nobody knows how April fool's Day started. Perhaps it was to celebrate the start of spring.