After the header, the page is read line by line, and the start of each line decides what it is:
| A line starting with | is |
|---|---|
# ## ### |
a heading |
* - or a number and . |
a list item |
> |
a quote |
``` |
the start or end of preformatted text |
--- alone |
a separator |
::: and a type word |
the start of an extension block, such as a form |
| anything else | part of a paragraph |
| nothing (blank line) | the end of a paragraph |
Inside paragraphs, headings, quotes and list items you can force line breaks and center the whole block.