Ulysses

The Ulysses App (available in the App Store) is a great all-purpose writing app, and works exceedingly well if you want to give your whole writing life over to it—which really wouldn't be a crazy idea if you have relatively standard needs as a writer). Even if you do have more specialized needs (the need to commit .md files to multiple different git repositories, say, or need to embed videos and interactive elements) you can still use it for a large chunk of your workflow.

good stuff

• one stop shop for organizing, drafting, previewing and exporting (to web, print, etc.)
• slick interface
• there's an iOS app too

drawbacks

• doesn't cope with YAML front matter (which is suboptimal if you are creating files for a Gatsby page, say)
• takes away control of file-naming (it simply names the file after the first line, minus any # tags — which also means you can't even really use a YAML if you want reasonably-named docs)
• subscription = $$$ you may not want to spend

tutorials

This is a pretty intuitive app, but if you are looking for a quick tutorial, this one isn't bad.