This is pretty straight forward.
You probably remember this from when you were a kid. But, in case you forgot, here ya go.
Click on any card. When it flips over, take a guess where it's identical pair is.
As you progress, try to remember where the cards are so you can get back to them.
Once you match all the cards, you WIN.
Great. Time for a Scooby Snack. ™
Or should you eat that before playing?
Either way, ENJOY.