I'm right handed, so I use my left hand to hold the yelper (wingbone, Jordan or trumpet). Each caller has it's own characteristics, but for the most part, I hold the end of the call with my thumb and pointer finger and close down my other three fingers as a sound chamber. Often, when I'm hunting, that's all I ever use is the one hand. Left hand holds the call, right hand holds my gun on my knee. If I'm in a situation where I don't have to worry about being seen, I cup my right hand around my left for a bigger sound chamber and more volume and more calling options.
Just play around with each call. They are all a little different and all have a certain way they like to be played. It's not rocket science, have fun with it.