To indent a paragraph in HTML, you can use CSS to apply the text-indent property, which allows you to control the amount of indentation for the first line of the paragraph. Another option is to use a CSS class, which you can apply to multiple paragraphs for consistent formatting. While it’s possible to manually insert spaces using non-breaking spaces, this method is less efficient and not recommended for good web practices. Using CSS is the preferred and cleaner method for indenting paragraphs.