Select, then pick a style
Select a few words and pick a style from the menu that comes up: Bold, Italic, Strikethrough, Highlight, Code, or Link. On the web the menu appears over the selection; on iPhone, iPad, and Android the styles are under Format in the selection menu, and on the Mac in the right-click menu. (In a phone browser, use the toolbar.)
The toolbar
Every app has a formatting toolbar: above the keyboard on iPhone, iPad, and Android, and at the bottom of the editor on the Mac and on the web. Tap a button to style the selection, or tap it before you type and keep writing in that style. Buttons light up to show the formatting at your cursor.
Choose which buttons come first: open the toolbar's More menu and pick Edit Toolbar (iPhone, iPad, Mac, and Android).
Add anything with /
On an empty line, type / to open the insert menu: headings, lists, a checklist, a table, code, an equation, a divider, an image or a file. Keep typing to filter, then pick one.
From the keyboard
With a keyboard, Cmd+B (or Ctrl+B) is bold and Cmd+I (or Ctrl+I) is italic.
Underneath, it is Markdown
Every style is saved as plain Markdown, so your notes open in any other app. If you already know it, you can type it directly:
**bold** *italic* ~~strikethrough~~ ==highlight== `code`