DoCoMoMo (short for "Documentation and Conservation of Buildings, Sites and Neighborhoods of the Modern Movement") is an organization that helps protect and preserve important buildings and architecture from the 20th century. They believe that buildings from this time period are important to our history and culture, and they want to make sure that we don't forget about them or destroy them.
Think about it like this: if you were playing with your toys and you had a really special toy that your grandparents gave you, you would want to make sure that toy was safe and taken care of so you could play with it forever. That's kind of what DoCoMoMo does, but with important buildings instead of toys.
DoCoMoMo has teams all around the world that help identify, document, and preserve modern architecture. They even have events and conferences that bring together people who care about these buildings and want to make sure they are taken care of.
So, in summary, DoCoMoMo International is a group of people who want to make sure that important buildings from the 20th century are protected and preserved for future generations to appreciate and enjoy.