He was sitting on a rock and played his PokéFlute, which causes any Pokémon to wake up. He played his song in exchange for money or food. Ash and friends needed his help to wake up a Snorlax that was blocking the river. He woke it up and moved out of the way, only to have the river blocked by more thorns. Snorlax ate the thorns, and then it went back to sleep.
Hippie saw Snorlax occasionally and played his lute to wake Snorlax up, as it was blocking the river.