You have to insert a few lines of code? For example here it is not clear if you have to put the Id of the publisher or the ad unit Id (web site MoPub)
<img src="http://imagizer.imageshack.us/v2/800x600q90/547/dw82.jpg" border="0" />
In addition, proceeds from where the ad unit Id created on MoPub to insert it here (Cocoonjs):
<img src="http://imagizer.imageshack.us/v2/800x600q90/203/djoj.jpg" border="0" />