* Vermilion City: Use Flash in the SS Anne, particularly in the areas where you can't see clearly. This is helpful for finding items or battling trainers.
* Rock Tunnel: Flash is essential in Rock Tunnel. It allows you to see in the dark and locate hidden items.
* Underground Path: Flash is needed here too, as you navigate the darkness. You'll find rare Pokemon and items with the help of Flash.
* Power Plant: While you may not need Flash to see everything, it can still be useful to help you navigate and spot enemies.
Important Note: Flash is a HM (Hidden Machine) move. This means you can't teach it to any Pokemon directly; instead, you must find a TM (Technical Machine) for it. You'll likely obtain the Flash TM around the time you're battling the third gym.
Let me know if you have any other questions about Pokemon Fire Red!