This is the old sliding tiles game.
The first two buttons at the top reset the puzzle to normal (numbers in order) and inverted configurations.
The inverted configuration is the same as the normal but with the last two numbers switched. There is no sequence of moves that will get the puzzle from the inverted configuration to the normal one.
The last button makes about 100 random moves, in effect scrambling the puzzle.
To slide the tiles, click on the tile that you want to move into the empty space. The arrow keys work too if keyboard focus is within the applet.