The 21st Century Cures Act is a set of rules that grown-ups made to help doctors and scientists find cures for really bad sicknesses. Sometimes, grown-ups get sick with diseases that there is no known cure for - that means they don't know how to make the sick person better. So, the 21st Century Cures Act gives lots of money to doctors and scientists to help them find new cures or treatments for these kinds of diseases.
Basically, the 21st Century Cures Act is like a big toolbox for people who want to help sick grown-ups. This toolbox has lots of new tools that can help doctors and scientists figure out how to make sick people feel better. It also has lots of money, so that they can do their work and find new cures and treatments faster than before. All of this will help people who are sick get better faster, and stay healthy longer.