Structure your text with HTML elements for paragraphs, headings, and lists. Choose a suitable formatting style, then inspect the markup in the result pane.
A webpage fragment, a full document, and an email have different requirements. Pick the appropriate style above the text panes and check the result in its intended renderer.
Generated HTML still needs the validation and sanitization required by your own application. The result pane displays it as text so you can inspect it before use.