In this video you'll see and hear a monk telling part of the story of the life of the Buddha. This video was recorded in Phnom Penh in 2006. Specifically, this is the episode where the young Siddhartha journeys outside the palace for the first time and encounters the four types of people--an old man, a sick man, a dead man and a monk--who are to play a key role in getting the wheels turning in his head about human suffering, the cycle of death and rebirth, and how we might escape that cycle.
There's a complete transcript to the monk's story in your textbook, page 91. There's some difficult vocabulary in the monk's version, most of it royal. You can find a list of these words on textbook page 92. But for the most part this oral version of the story is pretty straightforward.
Make sure you understand everything the monk says clearly, because you're going to be able to tell the story of the Buddha's enounters with the four types of people yourself, in Khmer!