Cutie Marks tell you the special talent of a pony. For example, the candy cutie mark on the picture may mean they are good at making candy. Or it could mean something else involving candy.
Some Pony Cutie Mark's are:Edit
Fluttershy's Cutie Mark shows that she is excellent with animals, such as butterflies.
Rainbowdashes cutie mark shows that she controls the wether.