Okay kiddo, so you know how sometimes when people don't agree on things, they form groups with different ideas about how things should work? That's what happened in Russia a long time ago, when there was a big group of people who wanted change in the way the country was run.
This big group was called the Social Democratic Labour Party, and they split into two smaller groups because they couldn't agree on how to bring about the change they wanted. One of these smaller groups was called the Mensheviks.
The Mensheviks believed in working with other people and groups to make changes happen gradually over time. They thought that it was important to have an organized group with a clear plan, and that everyone should have a say in how things are run.
The other smaller group that split from the Social Democratic Labour Party was called the Bolsheviks. They believed in more radical change and were willing to use more extreme methods to achieve their goals, like violence and revolution.
Eventually, the Bolsheviks became the dominant group in Russia and formed the Communist Party, while the Mensheviks lost influence and disappeared as a political force.