What You See Is What You Mean (WYSIWYM)¶
Markdown is a language based on the paradigm called "What you see is what you mean" (WYSIWYM, pronounced /ˈwɪziwɪm/). This means that Markdown allows you to define the structure of a text (e.g., define headings, bold text, blockquotes and links) but not what it looks like. Markdown files need to be processed further for publication. In short: Markdown files are "raw" files that require to be compiled into a final format for publishing.
This means that Zettlr is not a WYSIWYG-editor such as Microsoft Word or LibreOffice, and therefore does not display a layouted version of your text. Instead, it will show you the structure of your text. However, it will attempt to pre-render a few elements which are easier to work with in such a state. For instance, it will pre-render Markdown links, as it is easier to proof-read your text when the linked URL is out of the way.