Modifying a page is as simple as changing the _index.md file inside a folder.
\ content
_index.md <-- this here
\ Subfolder
_index.md <-- or this one
\ Subfolder2
_index.md <-- or even this one too
Hugo uses Markdown to format and style text, among other things.
You can find more information on how to use Markdown Syntax here: https://daringfireball.net/projects/markdown/basics