When you need to use fresh ginger, you need to peel it first before you can grate it for your recipe. Because ginger is very knotty and bumpy on the outside, you can waste a lot of ginger simply by grating it down so the skin is removed. Not to mention the risk of grating your skin too, as the grater hits each bump.
An easy way to peel ginger is to use a regular spoon. Hold the spoon facing towards you, slowly drag the edge of the spoon across the ginger to peel the skin.