Yes, the query string can help Google understand the meaning of the page.
What is important in the query string that displays unique content when the parameter value changes.
Example:
google.com/index.html?code=123123&footwear=shoes
google.com/index.html?code=123123&footwear=shoesB
If in this case you display the same content that may occur in duplicate issues. (You can also use the canonical URL)
It is best to rewrite the string as a URL such as
google.com/footwear/shoes/name-product-ID
Unique URL for each product.
Here is some useful duplicate problem resource
http://www.seomoz.org/learn-seo/duplicate-content