Simply put, it's pretty much the eBay of China.
Even though the website is available in Chinese only, there are third-party agents you can consult whenever you wish to buy something from Taobao.
Be wary of dodgy stuff on sale though. Last I checked, suggestions for whom one should buy from are of the following criteria:
-Seller's rating is at least 98%
-Seller's rank is at least two crowns (or maybe, diamonds? can't recall)
And do remember that Taobao takes no responsibility for dodgy items whatsoever.