Load your video, drag the brightness, contrast and saturation sliders while watching the live preview, then export the adjusted clip.
Yes, a live before/after preview updates as you move the sliders, so you can judge the look before committing to the full export.
Brightness shifts how light or dark the whole image is, contrast controls the gap between the darkest and lightest areas, and saturation controls how vivid or muted the colours look.
Basic correction can meaningfully improve a slightly dark or flat clip, but footage that is extremely underexposed or overexposed has lost detail that adjustment alone cannot fully recover.