A written quick start tutorial is available in the documentation.
And when you're done with the basics, move on to the advanced features tutorial.
The tutorials will also be available as video tutorials as I get done with them
For the particular pixel art style I used for the test tiles?
I'm not sure if there is a tutorial for it, I really just made it up as I went along. I'm not the strongest pixel artist so I'm not confident I can explain the decisions behind the tile set.