Paragraphs and headings are the building blocks of every web page that is smartly organized to provide information to readers.
In the Gutenberg editor paragraphs are – for good reason – the default block. Just click your cursor on the page and you’ll be in a paragraph block.
Headings are the way to let readers know the start of a new section of related content. Never use a heading for the purpose of making the font size larger.
Speaking of fonts when I show the paragraphs block options you’ll see there is no way to change the typeface. For that you’ll need to see what your theme offers or use a plugin to change font type.