Each Basic Correction slider works on a different part of the range. Exposure raises tonal values across the frame and stretches the highlights first. Shadows brightens the darker range and leaves the top largely alone. Blacks sets black clipping: left makes more of the image pure black, right makes less of it. Pushing Blacks to the right on top of a big Exposure move is a quick way to make a brightened clip look washed out.
For a typical underexposed clip, that adds up to a moderate Exposure increase, Highlights down to protect windows, lamps or sky, Shadows up to open the dark areas, and Blacks nudged left so the frame keeps a solid base. If the subject is dark against a bright background, the global sliders will fight each other; draw a mask on a second Lumetri Color effect in Effect Controls, or read our guide to brightening a backlit video.
Several clips from the same dark scene
Choose File → New → Adjustment Layer, drag the layer onto a track above the clips, select it, and grade it in Lumetri like any clip. Everything on the tracks beneath picks up the change. Even out the individual shots first, then put the shared correction on the adjustment layer, since the layer applies the same amount to every shot underneath it.
Noise: the cost of brightening
Brightening a dark clip brightens its noise too. Lumetri Color has no noise reduction control, and the Noise & Grain effects that ship with Premiere are designed to add texture, not remove it, so editors who need real denoising use a third-party plug-in. Without one, keep the shadow lift modest, let areas that hold nothing but noise stay dark, leave the Sharpen slider in the Creative section at zero, and go easy on saturation. Heavily compressed 8-bit phone footage has few shades in the shadows, and stretching them can show banding as well as noise.