What did Xian trade to get the silk?

Eden, Xian, called Chang'an in ancient times, was the capital of the Western Han Dynasty. It is the starting point of the road. China is well-known for silk. So there is no need for Xian to trade others in order to get silk. Instead, merchants take silk from Xian to trade with foreigners in the Western Regions.

But what did they trade to get the silk and what is the answer to who did Xian trade with

It was businessmen who traded on the routes. Peoploe from other regions got the silk by trading or exchanging fruits, vegetables, spices, etc.