(used to represent an inanimate thing understood, previously mentioned, about to be mentioned, or present in the immediate context): It has whitewall tires and red upholstery. You can't tell a book by its cover.
(used to represent a person or animal understood, previously mentioned, or about to be mentioned whose gender is unknown or disregarded): It was the largest ever caught off the Florida coast. Who was it? It was John. The horse had its saddle on.
(used to represent a group understood or previously mentioned): The judge told the jury it must decide two issues.
(used to represent a concept or abstract idea understood or previously stated): It all started with Adam and Eve. He has been taught to believe it all his life.
(used to represent an action or activity understood, previously mentioned, or about to be mentioned): Since you don't like it, you don't have to go skiing.