Well, a search for "Marketplace" would have yielded the
following result...
The Viewer Managed Marketplace (VMM) feature works similarly as in other viewers, with the exception that the "Marketplace Listings" being just another special folder in your inventory, the Cool VL Viewer lists it in the "Inventory" floater instead of hiding it there and using a special floater for the Marketplace. All the Marketplace related functions are also regrouped in the context menu for that "Marketplace Listings" folder and sub-folders.
Of course, you must first be registered as a merchant on the SL Marketplace website, and make sure that the "Hide Marketplace folder" item is not checked in the "File" menu of the "Inventory" floater.
Then, follow the instructions given in the
existing FAQ post.
Note that you might also see a "Merchant Outbox" folder appearing in your inventory: you can entirely ignore and even delete that folder (it does not serve any purpose any more but it reappears each time you relog into the Marketplace website due to a stale script in that site).