The only moves allowed are knight hops: two steps in one orthogonal direction, then one step at a right angle. The target position must be empty. (In challenge 2 you sometimes also have to click the desired target position if there is more than one.)

Challenge 1 has one empty square in the lower-right corner; challenge 2 has four empty squares.

The "select" buttons let you take back a move, return to the original scrambled board, go forward one move, or jump to the last move recorded.

Click the "reset to start" checkbox to return to the start.