To use a style, look at the formatting toolbar.
The first item in the box says Body Text 2, yours may say Body Text 1 or different. Click on the black downwards arrow next to it. A list of styles, headings and paragraphs appears. These are the styles that you are using in your document.
To create a style let’s go back to our text. Play with the heading until you
get a style you like using the font box. Format/Font.
To add a Style click on Format/Style
Click on the New button