Before the American Revolution, Britain sent over lots of soldiers to control the Colonists. These soldiers had to live somewhere, so they forced Colonists to let them live in their homes and to serve them. This made the Colonists angry.  This amendment basically states that soldiers can't force their way into your house and live there without your consent. However, during war, the amendment does make an exception. During war, soldiers can be quartered "as prescribed by law." So, during a war, if the US wants, they can put soldiers in your house.