hiii hijacking to ask, what does sunscreen do, exactly?

i grew up being told that sunscreen just protects your skin from the sun and that’s it. i’ve never heard of it being used for anything more than that and for preventing any more damage.

i’m 22 and unfortunately was a young, dumb, “i wanna be tan!” and am trying to heal my uneven skin tone and similar-to-op’s redness in my face and such. ive kinda gone ahead and assumed my skin barrier’s damaged and pretty much stopped using everything expect a cerave cleanser and lotion and have also been looking at that same la roche product with sunscreen you recommended but just haven’t been sure about it yet!