If you’re using WordPress.com then you can easily enable Markdown support in their online editor:
Enabling Markdown on WordPress.com
To start using Markdown, go to Settings → Writing in your blog dashboard, check the box next to Use Markdown for posts and pages, and save.
When writing Markdown, make sure to use the Text Editor for the best results.
Learn more from this excellent post Write (More) Effortlessly With Markdown.
If you’d like to learn about my Markdown history, check out this post:
Writing with Markdown for WordPress (on Windows)