A Marketplace is a place where all the trading pairs on Blocktrade.com exchange are listed.

Hoovering with a mouse over a preferred trading pair will show you two subcategories. Quick trade 

(Quicktrade explained), allowing you to quickly choose and opt-in for trade and Tradeview 

(Tradeview explained), where you can take a more detailed look at the graph and have additional trading options (limit order).