I recently gave a talk on the basics of Android drawable resources (via XML).
There's a recording I made of the talk - not super, but functional. I had to split it into two parts because of time restrictions on YouTube. Here's part one and part two.
I also have a few links that may be useful (whether you watch the talk or not):
- The slides for the presentation
- Official Android drawable resource documentation
- My drawable XML documentation
- The github project with my samples