The object of the game is to release fairies from their ice prisons and to progress from realm to realm before defeating Grendor. Spyro starts off in the Autumn Fairy Home one of the four seasonal fairy realms in the game. In the each realm, gems can be collected, critters like sheep can be destroyed for healing butterflies (and some to grant extra lives), special objects (like pumpkins) can be ignited and baskets can broken for more gems.
If the player collects 100% of all the gems and fairies from all levels and realms, they are granted the opportunity to enter a portal to play the extra game "Dragonfly X".
Source: Wikipedia, "Spyro: Season of Ice", available under the CC-BY-SA License.