How do you use adjustable choke on shotgun?

Many of the adjustable chokes are adjusted by turning the choke. (If it does not turn with moderate hand force, it is probably gunked up with carbon- let soak in a good powder solvent for a day or two and try again). They work by squeezing movable strip closer together, or further apart- the tighter the squeeze, the tighter the choke. A tighter choke holds the shot column together longer, and gives a smaller pattern that has greater range.