Okay kiddo, so the Residence Act was a law passed by the United States government in 1790. It basically decided where the capital city of the United States would be - which is now known as Washington D.C.
Before the law was passed, there was a lot of disagreement about where the capital should be. Some people thought it should be in the north, some thought it should be in the south, and some even suggested it should be somewhere in between. But eventually, the government decided on a special district that would be located on land donated by the state of Maryland and Virginia, which would become the capital city.
So, the Residence Act made it official and set a plan in motion to create the capital city in this special district. It also included instructions for how the city should be built and what kinds of buildings should be constructed there, like the White House and the Capitol building.
And that’s how the Residence Act helped create the capital city of the United States!