Imagine your family has two kids - you and your sibling. Your parents have different rules for each of you because you are different ages and have different needs. Similarly, one country, two systems means that there is one big country (like China), but two parts of it (like Hong Kong and Macau) can have different rules and systems.
For example, Hong Kong and Macau were once colonies of other countries but now they belong to China. However, they have their own legal systems, cultures, languages, and local governments. They are allowed to have some freedom and autonomy from China. Their citizens can enjoy some liberties and rights that people in mainland China do not have, such as freedom of speech, assembly, and press. They can also use different currencies, have different immigration policies, and maintain their own borders.
This is because of a policy called "one country, two systems" that was first proposed by China's leader Deng Xiaoping in the 1980s. It was designed to reconcile the ideological differences between China and the former colonial powers that governed Hong Kong and Macau. It was also meant to ensure a peaceful and gradual reunification between these places and China.
Although this policy has been hailed as a success in many ways, it has also faced challenges and controversies. For instance, some people in Hong Kong feel that China is trying to erode their autonomy and impose its own laws and values on them. They have protested and demanded more democracy and human rights. China, on the other hand, views these demands as a threat to its authority and sovereignty. As a result, the future of one country, two systems remains uncertain and subject to ongoing negotiations and tensions.