Head for Section G, Head to the Control Room, and Secure a Power Source are the first quests in Chapter 6, "Light the Way", in Final Fantasy VII Remake, taking place in the Sector 4 Plate. While Cloud Strife, Barret Wallace, and Tifa Lockhart travel to the Mako Reactor 5, they find their way to the Sector 4 plate where they are to meet up with Biggs.
A vending machine nearby sells the usual items, as well as materia, weapons, armor, and accessories, though none are new. A bench can be found where the player can sit to restore HP/MP, and as before, the player can use this opportunity to upgrade weapons.
Take the ladder down to a walkway, pick up the hi-potion in the treasure chest to the right, then follow Barret and Tifa across the walkway on the left. This leads to a wider platform with a door that cannot be opened; head across another walkway on the right (adjacent to the one used to enter) and climb the ladder to the control room. Interact with it, and a cutscene will commence, and Tifa will point out that sun lamps need to be deactivated to provide power. At the far end of the larger platform is a small ramp across to a sun lamp, with a ladder up to the console at the top. Pull the lever to deactivate it, allowing the party to proceed through the door on the larger platform.
Head through the door to Section G, commencing the following quest, "Head for Section H".