Welcome to the forum PD, Theres allot of diversity and info. to be found here as well as good people. I know nothing, of the dicovery 3300, I have a tracker IV, It suits me for being fairly new myself. Yes, you gotta dig some, to find some, I got the fiskars big handle garden knife, and a good trowel. Mine is cast aluminum.
You'll bend a cheapie in no time. Also get a probe, Just an old BBQ fork with the end broke off will work good, that way you can stick it in and feel kinda whats down there, . then dig away , I think you'll have to learn from experience, cause thats what it takes to learn you machine etc..
As far as your detector, take some coins out/ cover them with some books or cardboard,and , see what they sound like as you pass over them, use some silver and gold to if you have some. They all read differently and soon you'll be on your way, best of luck. smg