Text is added to a page with a text box. Text boxes can be inserted into a page body as well as the Header.

To insert a text box, navigate to the Insert tab from the panel to the right and select the Text box option. A text box will appear on the page with settings in an options bar above it. 

To change the text Style, click the first drop-down in the options bar. Style options include: Title, Heading, Subheading, Small, and Normal Text (default setting). Use these Styles to divide and organize page content. We recommend using text Styles to format the text instead of manually making adjustments with the font, size, and weight. Text Styles can be modified in the Theme (see Google Sites: Using Preset Themes for more details).