Early in the Resident Evil 3 Remake campaign, Carlos will tell you that you need to get the power back on in the subway, and to make your way to the substation. This is easier said than done, as the path you need to take is currently on fire. There is a fire hydrant close by, but you need a fire hose to put out the flames.
The first thing you need to do is turn back the way you came. Three zombies will knock down a fence, so take them out with a nearby red barrel. Head down the new path that they have opened up, and you will see Moon’s Donut Shop.
Go in the front door, then turn left and use the Safe Room beside the locker. Grab the ammo, gunpowder, and green herb, and make sure you examine the Fancy Box to get the red crystal.
Leave through the back door, and you will find more zombies in the street. Take them out with the red barrel, then head up the street a little to Kite Bros Railway. Head inside and follow the corridor, taking ou the zombie that will come around the corner. On the ground, around the right turn, you will find the firehose. Interact with it to put it in your inventory.
You can now head back to where the fire is and put it out, but first, go into the room beside where you found the hire hose. There is a Shotgun here that you cannot get yet, but keep a note of where it is for later. Examine the lockers, and you will find gunpowder and a hand grenade.
Remember to combine your gunpowders to make ammo, and combine your ammo to stack them all to save space in your inventory. You can now either continue to explore the area, or return to the fire and make your way to the substation.