What is Markdown
The wikipedia markdown entry introduced markdown as :
Markdown is a lightweight markup language with plain text formatting syntax. It is designed so that it can be converted to HTML and many other formats using a tool by the same name. Markdown is often used to format readme files, for writing messages in online discussion forums, and to create rich text using a plain text editor. As the initial description of Markdown contained ambiguities and unanswered questions, many implementations and extensions of Markdown appeared over the years to answer these issues.
Markdown in Deck
The Deck application plugin uses the markdown-it script to offer support for markdown in the cards description field.
Supported Markdown
Markdown comes in may flavors. The best way to learn markdown and understand how to use it, is simply to try it on the original script official playground.
That same link offers also a comprehensive list of what is supported, and what is not - rendering it unnecessary to duplicate that content in here.
CommonMark Markdown Reference
Known Issues
As per issue #127 Due to a known limitation of the current script to support markdown, Links that contain the ")" character will not display well, or will break.
The recommended solution is to use "<" and ">" to wrap those links. It should assure their integrity.
If you come by another case of broken link, or broken display of links, please report it by opening a new issue.