"That young police officer was pretty."
Translation:O genç polis güzeldi.
su means "water".
Where English only distinguishes between "this thing" (relatively close) and "that thing" (relatively far), Turkish has a three-way distinction: bu şey is close, şu şey is a bit further away, and o şey is even further away.
So "the police officer" could be either şu polis or o polis depending on whether he's a medium or a long distance away.