Through the fog, we could just barely make out land.
Literal
Fog [through-を通して], slightly land [object-を] make-out could-do [past-できた].
を通して = 'through X' — a compound particle for motion or perception through an obstruction. わずかに ('just a little, barely') emphasizes the minimal visibility. 見分ける ('to distinguish, to make out visually') is a compound of 見る + 分ける.