Try to guess the hidden combination of colours. You will be given limited information about each guess you make, enabling you to refine the next guess.
Drag from the colours on the left into the topmost unfilled row to make a guess; then click on the small circles to submit that guess. The small circles give you your feedback: black pegs indicate how many of the colours you guessed were the right colour in the right place, and white pegs indicate how many of the rest were the right colours but in the wrong place.