Formatting text with styles couldn't be simpler: You just select your text and select a style, and all the attributes of that style are applied to the text in one quick operation.
Help+Manual comes with a basic set of standard styles already predefined, so you can start using styles right away, even without defining your own styles. Normally, however, you will want to modify these styles and add styles of your own to create a customized layout and appearance for your project.
If you manage multiple projects that all need to look the same, check out Help+Manual's powerful style repositories. They allow you to share stylesheets between multiple projects and edit the styles for all of them in the same central location. See the Working with Style Repositories chapter for details!