Hugo-incorporated requires Hugo 0.12-DEV or newer. If your content is not displaying after running hugo server, be sure that your version (hugo version) is at least 0.12-DEV.
Markdown Content goes in content/post/title.md. Then:
hugo server -w
The stylesheet is included in static/css. If you want substantial customizations you should use the scss directory and install sass (and Ruby). At the moment, this is entirely optional, since I’m commiting the final stylesheet. Note that if you make customizations to main.css, then rebuild with sass, those changes could get lost.