The National Geographic link is definitely worth a look!
Measure the length and diameter of it. Look at the ground around it. Are there scratches in the dirt? Scat from another animal nearby?
See if you can tell what the animal ate (you may have to poke at it a bit, but try not to damage it too much so other groups can look at it too). Is there fur and bones in the scat? Berries and seeds? Plant matter? Is the animal a carnivore, herbivore, or omnivore?
How big is the animal? Sculpt the air with your hands to show how big you think the animal is. Look at the color and texture. If it is dark and moist, it is fresh; the animal was here not too long ago. If it is brittle and moldy, it is very old.
Draw the scat in your field notebook. Are there animal tracks nearby? Look it up to see from which animal it came.