On the Title Screen, wait a couple of seconds. Small multi colored stars and moons will then appear on the screen. Tilt the game boy left to move the stars and moons left, right to move them right, up to move them up, and down to move them down.
In 3-1 you have to go northeast from where you started to warp. To do this, jump the first bridge and get to the end. Go across the water to your right, and you will find a tree. He asks you if you want to warp to 6-1 from there.