Lots of great info passed along....
One thing of the utmost importance in learning to run a mouth call is finding the call, that fits You....Gobblenut nailed it in his post.
I'd recommend, starting with a double reed call for 2 reasons. 1. User friendly 2. Cost effective
Learn to make single notes of low, middle, and high FIRST, before trying to make turkey sounds...This teaches you air flow control, tongue playment, & a feeling for having the call in your mouth....
Teach yourself to call softly FIRST......Teaches air control & mouth calls are all about air control, when first starting to run them...PLUS, it ease household tension, when you sound like a dying seal at first....Over blowing a call will ruin it.....
Listen to "Calling all turkeys" for reference of what calls your going to practice, then call with the turkeys to compare your sounds to the turkeys sounds.
Be patient....Work thru the frustration & practice, practice, practice....15 min sessions of practice will limit your frustrations....
Good luck....