At the start of the Resident Evil 3 Remake campaign, Carlos will tell you that you need to turn the power back on in the subway and get to the station. This is easier said than done because the path you need to take is on fire right now. There is a fire hydrant nearby, but you need a fire hose to put out the flames.
The first thing you need to do is go back. Three zombies will knock down a fence, so take them out with a red barrel nearby. Go down the new path they opened and you will see Moon's Donut Shop.
Enter the front door, then turn left and use the safe next to the locker. Grab the ammo, gunpowder, and green grass and make sure to examine the fantasy box to get the red crystal.
Walk out the back door and you'll find more zombies on the street. Take them out with the red barrel, then walk up the street a bit to Kite Bros Railway. Go inside and follow the hallway, picking up the zombie that will come around the corner. On the ground, around the right turn, you will find the fire hose. Interact with it to put it in your inventory.
You can now return to where the fire is and put it out, but first, go to the room next to where you found the rental pipe. There's a shotgun here that you can't get just yet, but write down where it is for later. Examine the lockers and you will find some gunpowder and a hand grenade.
Remember to combine your powders to craft ammo and combine your ammo to stack them all to save space in your inventory. You can now either continue exploring the area or return to the traffic light and head to the substation.