Came across this recently.
The screenshot you've got there is exactly what I was getting, It can be solved by disabling your browser Ad block (I use AdBlock), there should be a load of info there and fields to fill in but with AdBlock or similar active it blocks them!
Secondly, MoPub is like a wrapper for ads. You pick a network, such as AdMob, then enter that info intpo MoPub, and MoPub will display AdMob's ads.
MoPub is largely for use with engines such as Construct 2 where there is no low-level or SDK integration.