Please review template.md for a sample layout and structure of a post. You can use standard Markdown to write your material (which includes HTML as well, see Daring Fireball's syntax guide for Markdown for more information).
There are also some specific Jekyll related formatting and syntax you can use such as highlighting code blocks, read Jekyll's documentation for help. Jekyll makes use of the Liquid templating language. You only need concern youself with small amount of its documentation.
The RSS feed is automatically built from the list of posts and added to feed.xml. Can be accessed by /feed.xml.
Please use the date formatting "FullYear-Month-Day" for both the naming of files and/or the date within the post's YAML, example file name: 2014-08-18-title-of-post.md
_includes/contains snippets that are included upon generation of the site itself in the layouts. This involves the<head>, site header, navigation, and footer (only seen at bottom of individual post page). Changing these will change them throughout the site._layouts/contains the two primary layouts that build the structure of the site itself.default.htmlis the base structure which everything is built off of.post.htmlis the structure for individual posts.main.cssis the primary stylesheet for the entire site.syntax.cssis the stylesheet for code blocks (<pre><code>). Please refrain from modifyingsyntax.css._data/contains YAML files that are used site wide, such as the Navigation or the Officers. Used by writingsite.data.yamlfile._config.yamlcontains all the important variables for the site itself. Such as where the build destination is, title of the organization, and more.