You can edit Markdown and view rendered Markdown all from within Notesy. A default CSS template used when displaying rendered Markdown is provided. You can modify this default template, or provide the path to other templates to load.
Notesy uses the Sundown implementation of Markdown with the table extension enabled. You can find the Markdown syntax here: http://daringfireball.net/projects/markdown/syntax. You can find an example of the table syntax here.
With Notesy's URL scheme feature, you can even use Notesy as a Markdown renderer from other apps. See an example of how to do this in the URL Scheme documentation.