There are various ways to tell if a diamond is real or fake, including the fog test, the water test, and using a jeweler's loupe to inspect the stone. However, the most accurate way is to have it examined by a certified gemologist.

The Four Cs stand for Cut, Color, Clarity, and Carat. They are important because they determine the quality and value of a diamond. Cut influences how well the diamond reflects light, color refers to the presence of any color in an otherwise clear diamond, clarity refers to the presence of internal or external flaws, and carat refers to the weight of the diamond.

The shape of a diamond refers to its physical appearance (round, oval, princess, etc.), while the cut refers to how well the diamond has been cut from its raw form. The cut affects the diamond's brilliance, or how well it reflects light.

Diamond grading involves evaluating the diamond based on the Four Cs. This is typically done by a certified gemologist in a lab environment. The diamond is thoroughly examined under magnification and different lighting conditions to accurately determine its quality.