How do I access the global market in SimCity?
The global market tab was originally designed to be a part of the Sim City World window next to the "Leaderboards" and "Challenges" tabs but it was removed before release of the game.
Here is a pre-release version of the window:
Currently it appears that prices of goods do not fluctuate on the global market although on release day the prices were fluctuating seemingly randomly so it is likely a feature Maxis is tweaking to reduce server load.