Here's what happens:
* Pippin is curious: Pippin is drawn to a mysterious, glowing object in the field.
* He breaks a fence: He climbs over a fence to get closer, accidentally breaking it.
* He discovers the Palantir: The glowing object is a Palantir, a seeing stone. He touches it, and it shows him visions.
This event leads to a lot of trouble for the hobbits, as the Palantir is a powerful object that can be used for evil.