Kingdom is a solitaire game. The rightful king has been killed by a usurper. You are a farmboy who is determined to get revenge for your beloved king.
You must travel to several different areas of the kingdom and solve problems for the inhabitants there. By doing this, you can eventually raise a mercenary army to overthrow the usurper.
Typically, the game uses a pickup and deliver mechanic. You will identify what the inhabitants of a certain area of the Kingdom need, and then find and bring that item to them. (You need to remember what they need since there is no reminder when you leave their area.)
The game does not use typical movement rules. You are free to travel from anywhere in the kingdom to anywhere in the kingdom on your turn.
You win the game by raising the mercenary army and moving into the castle.