When granulated sugar is slowly heated, it melts and turns golden brown. This process is known as caramelization.
The sugar must be melted in a heavy pan (not iron) over very low heat. Pour it into the pan (Step 1) and stir constantly with a long-handled spoon. The sugar will become lumpy (Step 2) as it begins to melt.
After a few minutes the sugar liquefies, turning the color of straw. If you continue to heat it, the sugar will turn deep brown, then will become black and burn.
To halt the caramelizing process, remove the pan from the heat and stir in one-quarter cup boiling water (Step 3), or the amount called for in a recipe. Because of the temperature difference between the sugar mixture and even boiling water, it must be added slowly to keep spattering to a minimum (Step 4).