The choke on a shotgun "chokes" the end of the barrel, compressing your shot. Therefore creating a tighter pattern. Kind of like a nozzle on a hose. If you turn it on without a nozzle it will come out thick and not go very far, put a fine tipped nozzle on and the water will stay together and travel farther. Hope this helps.
By opening up or constricting.
Yes, they describe the various chokes.
Modified.
Chokes for shotguns shrink the bore's diameter to tighten the shot pattern and increase practical range.
they help with patterns of shot and accuracy of slugs
A good basic article on chokes http://www.ssaa.org.au/stories/shotguns-a-beginners-guide-to-shotgun-chokes.html
Try e-gunparts.com
Refers to the amount of constriction at the muzzle.
Herter's sold various maker's products with their name on them.
Yes chokes are designed to tighten shot patterns.
I paid 425 with the camo , the slugbarrel and chokes
With standard chokes, Full Choke is the tightest. However, there are non-standard chokes for SOME shotguns (used by turkey hunters) that are Extra Full Choke.