the basic principal as i understand it (as a keen amateur) is it removes oxidants from the surface of the paint, tar, fallout and traces of other contaminents that washing cant get toas they're bonded to the suirface(clearcoat) of the paint. this leaves a better surface for the polish to "work" with and overall then gt a better finish.

it wont remove swirls no. you'll probably have to machine polish it for that. autoglymn super resin polish (srp) is full of fillers and will do a pretty good job of masking them short term though. i really dont recommend you go at it straight away with a machine polisher though. it'd be like taking your driving test on a rally stage you can do ALOT of damage with it.