Understanding URL Parameters Report in Google Webmaster Tools?

[onlinesource]

My URL Parameters report is showing up with a ton of responses including "dispatch" tied to 5567 urls and "items_per_page" tied to 2,260 pages. There are a lot more. I'm getting a ton of duplicate content flags with my shopping cart due to parameters like "items_per_page".

Not sure how to best address this? GWT is asking me if this content is seen by the user. I say YES, because since Google is scanning it obviously it does. Then it wants to know if I want to sort, narrow, etc.

Baffled here. Can anybody explain how this works?
.

[edited by: Robert_Charlton at 7:20 am (utc) on Jan 3, 2014]
[edit reason] fixed typos [/edit]

[aakk9999]

To handle parameters such as "items_per_page", the first question is whether URL without this parameter is internally linked to and produces a default listing.

a) If there is a URL without this parameter and you are linking to it internally, then I would select "Narrows" and then select option "No URLs".

b) If you cannot have URL without this parameter, then pick the one to be a "master" (the one you are linking to internally) and then select "only URLs with value of" and enter the value.

For example, if you internally also link to URL without the parameter:

http://example.com/product-listing
which by default shows 10 items per page when no parameter specified, and this is your URL that you internally link to

http://example.com/product-listing?items_per_page=20
which is URL that is created when the user selects 'show 20 items per page'

then this would be the situation a) above

On the other hand, if you ALWAYS have items_per_page parameter:

http://example.com/product-listing?items_per_page=10
where parameter MUST exist but 10 items per page is a default that you link to internally when first listing products

http://example.com/product-listing?items_per_page=20
which is URL that is created when the user selects 'show 20 items per page'

then this would be situation b) and the field next to "only URLs with value of" would be set to 10