Hey kiddo, do you know what a community is? It's like a group of people who live together and work together for their mutual benefit, like your family or your classmates. The European Communities Act 1972 was an agreement that the United Kingdom (UK) made with other countries in Europe to form a community called the European Economic Community (EEC).
This agreement said that the UK would follow the rules made by the EEC and work together with other European countries to improve their economies. It meant that people and goods could move more freely between the UK and other European countries.
The agreement also set up a court called the European Court of Justice to resolve any problems that might come up between the UK and other European countries. This court could make decisions that affect the laws of the UK, which is why some people have concerns about it.
So, to sum it up, the European Communities Act 1972 was an agreement that the UK made to work with other European countries to create a community and improve the economy. It meant that people and goods could move more freely between countries and a court was set up to resolve any problems.