A house is a place that people live in. Normally a family lives in a house, but sometimes houses are shared by friends or a couple. When you are talking about your own house, you call it your home.
A hutch is a cage or coop for small animals. Pet rabbits and guinea pigs are generally kept in hutches.
An igloo is a house made from blocks of snow. They are made by people who live in very cold areas, such as Inuit Eskimos and the people in Canada's north and Greenland.
A keystone is the stone at the top center of an arch. It holds all the other stones in place, which is why it is called the keystone. Keystones are often decorated quite elaborately.