Clousers are standard baitfish imitations. They are useful world-wide. The fly actually rides upside-down, except in Australia where the fly is right-side-up and the fish are inverted. (Just kidding about the Australia part.)
There are as many color variations as there are baitfish species. The basic idea is that the wing goes over and under the eyes. For saltwater, use a 811S hook.
How to Fish
Count-down-and-retrieve and slow retrieve presentations for lakes or slow/slack water portions of rivers. Vary the retrieve until you find what works best at the moment: slow and steady, fast, strip-and-pause, or quick, short two-inch strips. Also, wind-drifting works well in lakes. Where there is current in a river, you can also use a wet-fly swing with occasional twitches or strips.