The first part introduces Pi and his interests. We learn from this section that Pi is interested in zoology and religion. Pi attempts to combine the three religions together and is confronted by the imam, pandit, and priest. His parents eventually relent thinking that this is just a phase for him.
Part Two is the part where the boat sinks and Pi is stranded on a lifeboat with a tiger, an orangautan, a hyena, and an injured zebra. The hyena devours the zebra and orangautan, and later the hyena itself is killed by the tiger. Pi has to find a way to appease himself and the tiger. He later meets a blind Frenchmen, who tries to take advantage of Pi. Unfortunately, he steps into Richard Parker's (the tiger) territory and is killed.
In Part Three, two agents from Japan are investigating the matter and come to Tomatlan, Mexico, where Pi was washed ashore. They find his story hard to believe as they continue questioning him. They write a report at the end that concludes that the ship sank because of internal problems, concluding using only Pi's description, because all the evidence is now at the bottom of the Pacific Ocean.
There I hope this helps!