It's like a jigsaw puzzle, and a pretty easy one at that. Read to the end of this hint for a picture of the assembled cat if you're having trouble.
Hint 2
Pick up the pieces by left-clicking on them and rotate them by right-clicking. When you get any two pieces together, they'll lock and become a single piece you can move around.
Hint 3
The figure is a cat sitting down, with its hindquarters at the lower left and its head at the upper right.
Hint 4
I find it easiest to do the hindquarters first, since the cat has its tail wrapped around itself, and the tail is pretty easy to spot.
Hint 5
There are two versions of this puzzle, one for Amateurs and a more difficult one for Masters.