Click New Game to start the game, a decimal number will appear to the right of the Decimal: label. Click on one or more of the binary tiles (left of the = sign) to toggle them on (1) or off (0) until the sum of the decimal values of the "on" (1) boxes equals the Decimal value currently being displayed. Once the sum of the binary tiles equals the Decimal value displayed, the word "Correct" will appear, then click on the New Number button and a new Decimal value will appear. Continue solving the the decimal to binary conversions to see how many correct conversions you can achieve in 60 seconds.
Tip: you can also press the (Enter) key on your keyboard instead of clicking on the New Number button.