Okay kiddo, a dummy corporation is like when you play pretend and pretend to be someone else. But instead of playing with toys, grown-ups can play pretend with a company. They create a new company with a fake name and use it to do things they don't want to do under their real name.
It's like when you make a fake birthday party invitation so you can invite some friends you really like, but you don't want the other kids in your class to come. The fake invitation is like a dummy corporation, it's not real but it lets you do things without people knowing it's really you.
The grown-ups can use the dummy corporation to hide sneaky or secret things they are doing. It's not always a good thing, some people use it to do bad things. But sometimes, it can be used for good things like protecting your personal information or privacy.