Most likely you will need to apply formatting to specific text within a paragraph. For example, you may want to add topic links, conditional text, glossary terms, or keywords to enhance your help files. Character styles allow you to format text and apply D2HML styles to create these types of hot spots and more.
Just as with paragraph styles, any character style that has special help-authoring behavior should have a matching style in the Doc-To-Help project in order for it to work correctly in your help target. Doc-To-Help provides a large variety of predefined character styles, so you do not usually need to create your own. For more information, see Using Character Styles and Doc-To-Help Markup Language (D2HML).