If you're talking about the Sevii Islands, and you're talking about LeafGreen, just go to Vermilion and talk to the guy on the dock. He'll ask you which of the islands you want to go to.
If you actually ARE talking about Pokemon Green, which is unlikely, because it's a Japanese-exclusive game that isn't even sold anymore, I assume it's the same thing, or at least similar. Pokemon Blue and Red (english) are based on Pokemon Green and Blue(japanese), and Pokemon FireRed and LeafGreen are based on Pokemon Red and Blue(english). Maybe some lost in translation stuff going on, but you'll figure it out.
Chat with our AI personalities
You get the Rainbow Pass from Bill in order to have access to the other four islands in the sevii islands.
Usually you can find it in seafoam islands.
Johto is inaccessible on Leaf Green although Islands Four to Seven contain Johto Pokemon.
Cinnibar island, Fuschia city, the Pokemon league and two island and the other islands.
use an escape rope or the TM dig