Revolution is when lots of people get really angry and want to change how things work. This happened in Russia in 1917. There were actually two revolutions in Russia that year. The first one in February got rid of the king (or Tsar) and replaced him with a new government. The second one in October was done by people who wanted an even bigger change, and they overthrew the new government and took over themselves.
After the new government took over, they wanted to make things fair for everyone. They tried to take away land from rich people and give it to poor people. They also tried to take control of factories and businesses from rich people and give them to everyday workers. But these changes were really difficult to make, and some people didn't like them. Some people wanted to keep things the way they were, and they started fighting against the new government.
So, from 1918 to 1923, there was a really long and violent civil war in Russia. There were two main groups fighting – the Reds (who were on the side of the new government) and the Whites (who wanted to go back to how things were before the revolution). The Reds ended up winning, and they stayed in power for years. They changed Russia so much that it became a totally different country.
Overall, the revolutions of 1917-23 were a really big deal in Russian history. They changed the country forever and had lasting effects on the rest of the world.