[Q] [APP] Good tutorial or wallpaper app

Hey guys,
I'm completely new to Android APP development (done some ROM development), and I was wondering if anyone knew of a good tutorial to start out with? The first app that I want to make would be a wallpaper app where it pulled the wallpapers from a webservice via an AJAX call or something of the like.
If there was a good open source app that does this already, that might be fine. But I would prefer a tutorial on building it myself.

Thanks guys!