Ignorance is just an opportunity to learn.
~ Me 
As noted in the responses, the sublists are indenting two or more spaces or a tab (which I do use since it’s quick and muscle memory).
And the rendering is indeed controlled by CSS (Cascading Style Sheet), essentially defining what the finished product should look like. Both @chrillek and I have posted on the topic on these forums:
Remember, Markdown is a shorthand “language” for HTML content/web pages. You type the content and the CSS styles it. The rendered content can be used in a variety of ways, including exporting to formats like PDF. If you didn’t need or care about the rendering, you’d just use plain text.
I also discussed different styling methods briefly in the Documents > Markdown Documents > Styling section of the built-in Help and manual.
… and a quick example (with internal styling)…
… and one a little more complex…
And again… if you don’t care if the color is red, the text is bold, etc., you could just use plain text instead.