Reddit mentions of A Field Guide to Genetic Programming

Online material: I don't know about any high-quality online-run courses, but with GAs (and EC in general) you'll get quite far with searching Google for "evolutionary algorithms filetype:pdf", or something similar. In addition to freestanding texts, there are many Unis that have courses on biologically inspired AI, with high-quality lecture notes available online.

Where to begin: A standard toy problem is "one max" (have your EA find the bitstring of all ones).
You can start with a pretty simple program, confirming that your EA can solve the problem, and then expand it into a flexible solution supporting multiple selection mechanisms, various representations (binary, real-valued, permutation-based, ...), development schemes, and nice visualizations. EA systems lend themselves quite well to OO design, although other approaches are possible.

Recommended dead trees: An excellent book on EC is de Jong's Evolutionary Computation: A Unified Approach. While quite short, this book, written by one of the absolute experts in the field, is very pedagogical, broad-scoped, and up to date. One problem, though, is that it it's somewhat short in its treatment of GP. If you're interested in GP as well (and who isn't?), you could get this little book which costs about 1 nickle.

Good luck with exploring Evolutionary Computing! It's an amazing subject. You can begin with a 20-line program that you can explain to a kid, and later find yourself reading grad-level mathematics exploring intricacies of some aspect of evolution. Just be prepared for some weird looks when you finally find yourself printing papers on "Incest prevention" in the school library.

Edit: Spelling.

This book might be a good start to get an overview.