Youtube has some decent calling videos on it for free. There's lots of online resources to ck out too. It's very important to listen to REAL turkey sounds (avail on this website, NWTF website, etc) and also understand what the different sounds mean, then watch calling videos for tips to mimmick those sounds and understand what you are "saying" with those calls, etc. Then practice, practice, practice. W/ mouth calls, I like to do it in my car to/from work so it doesn't drive my wife crazy. Do it throughout the yr, and at least the 1st month before season opener so you are confident, new calls are broken in, etc.
Knowing what to use, and when....all comes down to experience/time in the woods then. If you put in the "work", it'll come. Good luck!