Hong Kong is a big city in China that used to be controlled by the British. China got Hong Kong back in 1997, but there are still some people in Hong Kong who want to keep some of the rules and freedoms that they had when the British were in charge.
In China, the government makes a lot of the decisions, and people don't get to vote or speak out as much. In Hong Kong, though, people have more freedom to do those things.
So sometimes the people in Hong Kong get mad when the Chinese government tries to make them follow different rules. They think that the Chinese government is taking away their freedom.
The conflict happens because Hong Kong wants to keep some of their rules and freedoms, but China wants them to follow their rules. It's like if you and your friend want to play a game, but you both want to play it differently. It can be hard to agree on what the rules should be.