My two cents worth..................
Settings can vary depending on the salt content, black sand, and if your in the water or not. I personally never set my disc above 1.5 and my sen is set between Auto to 11-1, (based on clock positions) it all depends on how stable it is. I turn my volume to max, and my thresh to as soft as possible and still hear it. If I was to describe it, it would sound like a mosquito or bee flying.
Try Auto first, if you start getting a lot of constant false signals (constant squawking), move the sen clock wise till it settles down and becomes stable. Usually anywhere between 10-1 o'clock position. Don't worry about losing depth, it will still see plenty deep enough.
When you get a signal, sweep it left to right, then turn 90 degrees of target and sweep it again left to right. If you still have a good signal then dig it. Dig all signals till you learn the sounds. You will learn what pop-tops and bottle caps sound and act like. BUT REMEMBER, sometimes gold will make the same sound so if it was me, I would not skip too many targets thinking they are poptops. There is a chance your walking away from a nice gold ring.
Iron will null out and or sometimes you get a signal sweeping to the left, but none to the right, or you get a signal sweeping left and right, but when you turn 90 degrees you null out with no signal.
This is where a nice BIG scoop comes in real handy, your recovery of the target is fairly quick.
Practice, with it, but it's not hard, it took me no time at all to learn the tones, and I am not that fast.
Please remember, always fill your holes even on the beach. 