The Canadian Siberian Expeditionary Force (CSEF) was a group of Canadian soldiers who were sent to Siberia, which is a country very far away from Canada, to help out some other countries who were fighting in a war.
The soldiers went to Siberia because there was a big war happening in a place called Europe, and some other countries needed help fighting in the war. But, they couldn't just take soldiers from their own country because they needed those soldiers to protect their own country. So, they asked Canada for help and Canada decided to send some soldiers to help out.
The soldiers who went to Siberia were called the CSEF, and they went on a long journey through lots of different countries to get to Siberia. It was a really tough journey, but they finally made it there.
When they arrived in Siberia, the CSEF helped to protect some important places and people from other countries. They also helped to stop some bad people who wanted to cause trouble.
The soldiers stayed in Siberia for a while to keep helping out, but eventually, the war in Europe ended, and the other countries didn't need their help anymore. So, the soldiers came back home to Canada, where they were thanked for their hard work helping other countries.