how do i get from cerulean city to pewter?please

You can't well you can but it's way hard, you have to fix the problem , in the station or radio station , in vermillion city , then you can catch the slow poke, then opening the way to Cerulean city

For me it's really hard for the directions.. But try the train station...
Maybe it can helps..

You must go towards the cave East of Cerulean, go all the way to the end and DO NOT enter the cave. Instead, go to the top of the area and ride the water and make a right (the only direction you can go) all the way down until you see a big building and some grass. Walk in and talk to the guys there. Then leave the building and fly back to the Cerulean Pokemon center if you are lazy. Then walk into the gym and you will see a rocket member confused. You then walk out and go up towards Cerulean cape. You will face him and he will tell you where the missing power plant part is. Then you go back to the gym and get it. Then return to the power plant and give it to the manager of the plant. Then fly to Lavender and go into the radio station and receive a car that allows you to tune into Kanto music. Then walk south of lavender until you reach a sleeping snorlax. Go to your pokegear and tune into a station that plays a lullaby like song. Then exit the menu without changing. The Snorlax wakes up and attacks. I advise you catch it being the only snorlax in the game, thats just me. So as long as you defeat/catch it. A whole new cave/path is clear for you to get to pewter.

Lol I hate it because on the map it shows that if you go left then you can go to Pewter city, but you actually can't. I also hate that I can't get there because I need the TM Flash that I forgot to take.

Actually the best way is to go through digglets cave left of vermillion city