The Style and Formats drop-down menus allow you to change the formatting of any selected text. This includes various headings and things like buttons built into the theme. First select your desired text, then choose the option from the dropdown. The styles won’t be reflected in the text editor, but on the page.
In the Styles dropdown, Paragraph is the default selection. Please refrain from using Heading 1. There should be only one used on the page, and it’s already being used as the page title.
If you click on the Toolbar Toggle button on the far right on the toolbar menu, you will reveal more toolbar options and see the Formats dropdown. The Formats dropdown contains any additional styles available in the theme, and allows you to turn your links into buttons.