Firstly, כ is not a guttural letter, but simply a soft letter. "Guttural" means pronounced in the throat.
In modern Hebrew, they are pronounced the same, like a harsh scratching noise at the back of the mouth.
Originally, and how many Sephardim pronounce them, כ is pronounced in the same area of the mouth as hard kaf, with air hissed through a narrow opening. ח is pronounced by squeezing the throat muscles and exhaling, which is difficult for many English speakers to replicate.