The jigsaw will start with the picture broken up into pieces. If the mouse is moved over a piece, a highlight should be seen. It is then possible to move the piece by pressing the left mouse button and holding it down whilst "dragging" the selected piece.
If pieces need to be rotated the selected piece can be rotated by clicking the right mouse button (Note that this is not a true rotation, but a flip and mirror sequence).

The "Breakup" button does exactly that and breaks up the puzzle.
The "solve" button can be used to solve the puzzle.

When the puzzle is correctly solved, a message will appear on the top line. If this does not appear and the puzzle "seems" to be solved, it is usually because a piece is in the wrong place or is rotated into the wrong position.

It is possible to "lose" pieces under other jigsaw pieces (just like real life eh?). If this happens you should move the visible pieces one at a time to try and find the lost piece.

Each time the jigsaw applet is started (not when you use the breakup button) the jigsaw will be cut up randomly. This means that the pieces may be cut differently each time.