My post lives in
_posts directory. Go ahead and edit it and re-build the site to see your changes. You can rebuild the site in many different ways, but the most common way is to run
jekyll serve, which launches a web server and auto-regenerates your site when a file is updated.
To add new posts, simply add a file in the
_posts directory that follows the convention
YYYY-MM-DD-name-of-post.ext and includes the necessary front matter. Take a look at the source for this post to get an idea about how it works.
Jekyll also offers powerful support for code snippets: