...you may not have seen anyone mention the AdWords Learning Center. This is a pretty good free resource, as you come up to speed with what brings you good results with AdWords.
So you might want to take a look:
AdWords Learning Center
BTW, don't let the first sentence which mentions "the Google Advertising Professional Exam" throw you off (!), as the learning center may be used by anyone.
Here is some other stuff worth looking at, from the AdWords FAQ:
A whole bunch of keyword related help topics:
Demos and Guides:
Searchable Help Center:
I hope this info proves to be useful. ;)