From the dropdown in the the upper left choose Marketplace / Banner Ads (Not sure how to access BLOX Applications? Click here)

  Either create a new Ad or open an existing Ad (for help on creating/editing and Ad, see Quick Start Guide to Create an Ad or the Banner Ads Workspace document). 

AdMgrImpress_Default.jpg
AdMgrImpress_Balance.jpg
AdMgrImpress_SetCap
AdMgrImpress_Performance.jpg
AdMgrImpress_Save.jpg