The Lead Paragraph shows an opening paragraph in larger type, as the first lines of an article often are.
Adding the block
Under New Block, choose Lead Paragraph, write the text and save. There are no options.
On the public site
The text is wrapped in the theme's .v-lead class, at reading width. An empty block prints nothing. Use it once, at the top of a page; for a highlighted note in the middle of a page, use a Callout.