Peel the ginger and slice it paper thin (a mandolin slicer works best… make the slices as absolutely thin as possible). Place the ginger in a small saucepan, cover with water and bring to a boil. Boil for 1 minute and drain in a colander. Put in a clean (sterilized) jar. Put the vinegar, sugar, and salt into the (non-reactive) saucepan and bring just to a boil, stirring to dissolve the sugar and salt. Remove from heat and pour over the ginger slices. Marinate at least one hour (I usually don't dig in for a few days). Keeps indefinitely in the refrigerator.
You can add a single drop of red food coloring if you want to give it a pretty pink blush.
Since young ginger is superior to the usual ("old"??) ginger and is seasonal, I usually double or triple the recipe so I'm stocked. It only gets better with time.