Harvesting Garlic?

I planted one bulb of garlic in late May that I had leftover from the store to see if it would grow- I put it about 3 or 4 inches under the soil and on a slope that gets part sun and shade. To my suprise, it grew and the leaves are about a foot tall! The leaves are starting to turn yellow and wilt- when do I know to take the garlic out? I stopped watering it. And how do I "dry and cure it"? I have been looking at some websites but I was wondering if anyone could help me out more...