Okay kiddo, so a long long time ago, there was a country called Poland. It was a big country, but it had some problems with other countries nearby. These nearby countries, like Russia, Prussia, and Austria, wanted to take some of Poland's land for themselves. So, they decided to split Poland into pieces, or "partitions," and each country took a piece for themselves.
Imagine you have a big toy castle, with lots of rooms and walls. Your friends come over and they decide to split your castle into three parts. You give one friend the tower, another friend the main hall, and the last friend the kitchen. Each friend now has their own part of your castle and can do what they want with it.
This is kind of like what happened to Poland. Russia, Prussia, and Austria each got their own part of Poland to control and rule over. They could make their own rules and decisions for their part of the country, without having to listen to the Polish people or government.
This made things really hard for Poland, because they were no longer a united country with their own government. They had to follow the rules of the country that was ruling over their part of land. It was like having three different babysitters who all had different rules and ideas of what they wanted you to do.
So, in summary, the partitions of Poland were when nearby countries split Poland into pieces and took control of those pieces for themselves, making things difficult for Poland's people and government.