Well, while the question and answer editor have both

• their toolbar to choose formatting/link options via the according symbols and
• display "Markdown Basics" in the right pane,

you can also use the same syntax within comments, as documented here:

Markdown Help

Furthermore, in order to display formatted code as-is (say, for SQL statements, console log contents, query results), it's easiest to surround those with a

<pre> tag pair.

Note, sometimes the WYSIWYG preview below the question/answer editor does display things differently than the real view...

Over time I have drifted to raw HTML, especially in comments but also in questions and answers.

IMO the most useful tags are a, b, blockquote, img and pre. Sometimes br, h2, hr.

Tips

The width attribute of img is an easy way to shrink images; just width, not height, to force the browser to scale; for example img src="https://i.imgflip.com/1f05x8.jpg" width="100":

Use b together with a to make the links stand out.

Plus...

Don't try to fight the CSS used by this forum.
Just be happy it doesn't use Fiori :)