A choke constricts the shot as it exits the barrel. Different chokes constrict it more or less depending on the type choke. Basically you have improved cylinder on one end of the spectrum to XXXFull on the other end. There' s more to it, but that' s the basic. Improved cylinder for wing shooting, quail, dove etc.
For turkey hunting you want a tight constriction, Extra Full or XX Full usually. This gets to be it' s own science but that' s the short answer.