The instructions are said in the game but I will say them here too: Control the mouse with the arrow keys. Eat the muffins to gain points. Stay away from cats and ghost foxes! You can touch the portals, but it's usually best to stay away from them; the cats come out of them. I have discovered that if you press the arrow keys in a certain order, the mouse can walk backwards through walls. <sigh> Must debug!
I got the idea from a Scratch book I read, but changed a lot of things from their idea. The muffin is a cheese in their original idea, and the cats are beetles (I thought that cats would be more realistic). The maze I drew myself; as you can see, I'm not the best artist in the world, but I do what I can. ;)