You need the Poke Flute,You get it from Elder/Mr. Fuji but first you need to defeat Rocket-Gang/Team Rocket and save him in the Pokemon Tower which is in Shion/Lavender Town and he'll give it to you.
Play through the tower in Lavender Town, defeating the Cubone's mother (Marowak), then get the PokeFlute from Mr. Fuji and then use it when you are blocked on the way to Fuschia City... He will wake up and you will fight him, plus have the chance to capture him, if you are persistant enough to go through many Great Balls.
