Your first stop should be the Official Tutorial.
Then I would suggest looking at the Samples. The samples do a better job than the reference guide in showing how things should work.
After that, I’ve written an overview and set of examples for working with some of the concepts. One that is very useful to understand, and not always obvious, is setting filters and parameters prior to load.
Michael Kovner’s excellent set of examples of doing just about anything.
Russell Christopher’s amazing You Did What? examples