Mastermind is a game of logical deduction. The computer will think of a four-digit number, and you have to work out what it is.
Start by making a guess. Each of the digits in the number you guess will be marked BLACK or WHITE. BLACK means the right digit in the right place; WHITE means the right digit but in the wrong place.
So for example: if the number was "1 4 2 5" and you guessed "2 4 3 3", you would score a single black and a single white - a black for the "4" in the right place, and a white for the "2" in the wrong place. When you get it exactly right you'll score four blacks, and the game is over.
The overall objective is to get it in the fewest attempts.