The shockwave puzzles listed at the top are more difficult and can't be changed. The "java" puzzles are great for all ages because the difficulty level can be changed. Click on a topic then click on a puzzle name. Click on the "shapes" button on the menu to the left of the puzzle pieces to change the number from 6 to 247 pieces and to choose the shapes of the pieces. Each puzzle is timed so if you want to play for a best time click on the "shuffle" button to play again. If you get impatient, click on the "solve" button to watch the puzzle assemble itself!