Rotate square sections of the grid to arrange the squares into numerical order starting from the top left.
In the basic game, you rotate a 2×2 square section. Left-click in the centre of that section (i.e. on a corner point between four squares) to rotate the whole section anticlockwise. Right-click to rotate the section clockwise.
When you master the basic game, go to the Type menu to try it with larger rotating groups (for a 3×3 group you must click in the centre of a square to rotate the block around it). Or select the 'orientable' mode in which every square must end up the right way round as well as in the right place. Or both!