Sugar cane began to grow wild in India and south-east Asia about a hundred million years ago, when grasses evolved from earlier plants. When people first walked to India, about 60,000 years ago, they probably began to eat the sugar cane pretty much right away. For people who are using a lot of energy running and working hard, sugar provides a lot of carbohydrates - and it tastes good. Certainly by about 2500 BC, people in India were eating sugar cane. For three thousand years after that, though, only people in India and south-east Asia ate sugar cane. This was because you had to eat it fresh, before the juice dried up, and sugar cane wouldn't grow further north.
Then about 350 AD, under the Guptan Empire, Indian food scientists finally invented a way to make sugar cane juice into crystallized sugar (what you find in your sugar bowl). You did this by grinding or pounding the sugar cane to get out the juice. Then you dried the juice in the sun and you got lumps of sugar that would keep for a long time. Now Indian merchants could sell these lumps of sugar to other countries.
When Buddhist monks began to travel back and forth between India and China, they brought sugar to China with them. Emperor Taizong of the T'ang Dynasty got interested in sugar, and he asked official Indian ambassadors to come to China to explain how to grow sugar cane and make sugar. The T'ang emperors sent at least two missions to India in the 600s AD to learn more about sugar technology.
For more information about sugar, check out these books from Amazon or from your library: