How do you get to 8 and 9 island on fire red?

In Pokémon FireRed, you can access Islands 8 and 9 by using the Sevii Islands ferry service. First, defeat the Elite Four and become the Pokémon Champion. Then, head to Vermilion City and take the ferry from the dock to the Sevii Islands, specifically to Island 1. From there, you can navigate through the islands to reach Island 8 (Bamboo Island) and Island 9 (Navel Rock) by completing the necessary quests and using the appropriate boat services.