I'm gonna skip the introduction and get to the point of this post. The Chinese traded Silk to Europe for I'm not sure how long but long enough that the Europeans couldn't live without it. What did Europe have that the far east wanted in return?
Well according to Frederick C Lane the 'export' that the Portuguese offered in exchange for the India trade was "violence and protection"
See also By Warfare at Sea, 1500-1650: Maritime Conflicts and the Transformation of Europe By Jan Glete who writes that the Portuguese converted the idea of European seabome violence and protection as an export commodity
There were not many items produced by Europe itself which would have been worthwhile to haul over to China, except for gold and silver of course
However you have to understand that trade was not "bilateral" -- European ships could pick up something in for example Egypt and take it to China