Get the tube wrench out of the box and use it to screw the choke tube out of the barrel. All chokes look thin - choke is constriction, measured in thousandths of inches. The side of the tube should be marked with the choke: such as Improved Cylinder (IC or IMP CYL), Modified (M or MOD), Improved Modified (IM or IMP MOD), or Full (F or FULL). Those are the four main constrictions, listed from least to most constriction. Some companies will use * on the side or notches at the muzzle end of the tube, rather than writing, to denote constriction. Generally, but check the manual for your gun to be sure, one * or notch is F, two * or notches is IM, and so on.
Most gun makers recommend no tighter than a Modified choke for lead buck shot, and steel shot of any size, but check the manual for your shotgun. If you don't have the manual most companies have them available for free download on their websites in Adobe PDF format.
Once more - CHECK THE OWNER'S MANUAL