I shall put forward my response in point form:
1. definition - here is one from Google:
A street market is an outdoor market such as traditionally held in a market square or in a market town, and often held only on particular days of the week. Very similar markets, or bazaars, can also be found in large enclosed spaces, instead of on a street.
2. Examples in China - Panjiayuan in Beijing for antiques; Temple Street in Hong Kong for clothes and gadgets.
3. Other countries - plenty of information on the internet. Here is a link on markets in London
http://www.timeout.com/london/shopping/london-markets
If you have not been to markets in other countries, honestly tell your examiners so.
4. Exam techniques - your examiners would be looking for topical vocabulary and descriptive ability.
Topical vocabulary and concepts would include:
market days
temporary stores
local colour
community life
second-hand goods
bargains
creativity
individuality and sole proprietors
community aspirations
social trends and movements
a village market in an urban concrete jungle
tourism
counterfeit goods
government control
etc
Descriptive ability - try and evoke the atmosphere of a street market: the bohemianism, the noise, the trade, the range of sellers and buyers, etc
Socio-economic perspective - Is it a mirror of the larger society? Are there problems? What are the good points? Why can they survive?
This is a general framework on which you can build your preparation. If you do all the research and thinking suggested here, you will pass your exam with flying colours.