What's the difference between ic recess cans and non ic recess can and what locations there both allow to be used in

IC rated fixtures mean that insulation can be in direct contact with the housing.

Non- IC rated fixtures will state in the instructions that insualtion and combustible materials must be kept away, usually at least 3 inches.

As far as locations, other than the insulation issue, each fixture may be rated Dry, Damp, or Wet locations.