Cooking sugar, which is one of the basics of patisserie and sweet-making, is a delicate operation in which sugar is heated from 100°C or 212°F to 180°C or 356°F. Here is some information on this tricky subject.
[Translator's note: the terms used below correspond to the French tradition, as often used by English-speaking chefs, but there are other stages and terms in other traditions. Best to use a thermometer, and be guided by temperature, as the English terms commonly used in domestic cooking cover less precise stages, broader temperature ranges, and so could lead to confusion.].