The long text field can have rich text enabled for headings, lists, code apps, and text formatting (bold, italic, strikethrough). In the API, the input and output for this formatted text uses Markdown, a lightweight and readable syntax. Originally invented by John Gruber, today Markdown is a popular way to format text and there exist many dialects and extensions. Airtable supports a variant of Markdown that is similar to most Markdown dialect syntaxes, but tweaked for the rich text formats.
For more information on writing and formatting with Markdown in Airtable, check out the Markdown syntax for Airtable article.
To get an even simpler version of this text if formatting is not needed, a formula with just rich text will result in just the text and line breaks.