Sugar is a sweetner, it's one of the nice tasting foods that vegetarians can eat but too much is bad.
Sugar and health
Too much sugar in a diet can cause tooth decay. Sugar including honey can also increase the risk of many diseases including obesity, heart disease and Type 2 diabetes.  Health experts are concerned about the health effects of sugar in western diets. Experts disagree about the upper limit of how much sugar we should consume but there is general agreement that we should limit how much sugar we eat. Many other foods such as products made from refined wheat make it hard for the body to control blood sugar as does sugar itself. 
"Action on Sugar" in the UK recommends a woman should eat at most 50g (1.7oz) of added sugar per day. men should eat at most 70g (2.5oz). The American Heart Association advises men to eat at most 36 grams of sugar per day, and women at most 20. 
You shouldn't feel too much discouraged if you can't keep within recommended limits all the time, most of us are tempted by cakes, sweet biscuits and the like. The closer you get to a fully healthy diet the better it will be for you.