Admob mediation with Startapp integration?

Hi everyone. I'm trying to release my first mobile game with ads but i'm a little lost. I'm not a programer just a web developer. I manage my self to integrate Startapp really easy i must say. But i want to integrate admob as well.

Can anyone explain to me at least what are the basic steps to follow and if this can be achieved inside unity or if i have to build my game and integrate this 2 platforms on xcode and android sdk? is there any plugin/s?

Thanks a lot :)

===EDIT=== Before anyone answers this, i have already look the documentation for startapp mediation, admob, etc. but i don't really get it. I don't pretend a tutorial just to point me in the right direction and if you can enumerate the general steps to follow. If there is any plugin or tutorial already done for unity of course give me the link it will be appreciated