Slide the blocks to move the blue key block to the green exit area. Blocks can slide up, down, left or right into empty spaces. Only the key block can slide into the exit gate.
Use the mouse or a finger to drag the blocks around. A block follows the pointer and settles on the nearest space it can actually reach, so you can aim roughly and let it snap.
You can also play entirely from the keyboard. The arrow keys move a red cursor around the board. Press Enter or Space on a block to pick it up: it lights up, and the arrow keys then walk it one square at a time through the spaces it can reach, refusing any step it cannot make. Press Enter or Space again to put it down, or Escape to hand it back to where you found it.
However far a block travels in one journey, by drag or by keyboard, it counts as a single move — and sliding it straight back where it came from takes that move off again.
If you use Solve, it does not fill the board in; it marks the next block to move and outlines where it should go. Enter or Space then plays the route one move at a time. While a route is showing, those keys belong to it — make any move of your own and the route steps aside.
Generating a new puzzle takes a moment, and longer on the larger sizes — the generator solves the board from scratch after every change it makes, to be sure the puzzle it hands you is still solvable.