Modern paint is a clear layer over colour. Most of what you see as dullness, swirling or haze is not in the colour at all — it is fine scratching in that clear layer, scattering light instead of reflecting it.
Correction uses machine polishers, abrasive compounds and specific pad combinations to level a small, controlled amount of that clear coat until the surface is flat again. Flat paint reflects cleanly, which is what reads as gloss and depth.
Because it removes material, correction is finite. Every vehicle has a limited number of safe corrections in its lifetime, so how much is removed matters as much as the result.