.md has many variations (like OPML: emerging sister defacto tree_outliner) but once you learn the basics, native apps' variations/flavors can be learnt in a few minutes. Why .md matters:

# Many apps & growing

# Easy, in 15

# Many sys layers/platforms etc adopting it, static site generators, dynamics, Wikis & many more categories + platforms ...., are adopting .md

# Emerging defacto standard for flat files, though layers can be simulated on many apps using headers (headings levels)

# It's the future

https://www.markdownguide.org/cheat-sheet/

https://www.youtube.com/watch?v=NnCy7wJRgP0

Can try to learn with some of the best Markdown FOSS apps with dual panes to see the output preview as you type, like Joplin, see photo:

https://opensource.com/article/19/1/productivity-tool-joplin

https://joplinapp.org

Good luck.