From Wikipedia:
Tai Lung plans revenge to capture the Furious Five after the day he was defeated by Dragon Warrior Po. Whoever the player is playing as (Po and Tigress) they start training in the Valley of Peace. After their training, the player then goes to the front entrance of the village.
The player arrives and rescues Viper from the Wu Sisters.
After their defeat, Mantis is there, the player then journeys to rescue Monkey from Ox after General Ox's defeat.
When the player arrives at the arena for the final battle, the player rescues Crane, fights Tai Lung and defeats him.