Answer:
It's very simple. Just go to Pallet Town and walk to the south, until you reach the sea. Then just surf to the south until you reach The Cinnabar Island.
You can also go through Seafoam Islands, where you can also catch Articuno, but you can do it later though. If you choose this way, you will need a Pokemon that knows Strenght (HM04) with you. You can't manage through Seafoam Islands without Strenght, you need to move some boulders there. When you reach the other entrance of Seafoam Islands, just surf to the west, until you reach The Cinnabar Island. Remember buy an escape rope ant take it with you, just in case you will go totally mindfuck and get lost.