The Live Docs tab in Pluto lets you read documentation while you code. Julia has a built-in documentation system, which lets Pluto query the documentation of any Julia object.
While you are typing code, or when you select some text, Live Docs will automatically start searching for documentation. This means that you can just leave the window open, and it will quietly search documentation while you work. Whenever you need to know how a function works, just take a look at the Live Docs tab.
You can also search for documentation directly, by typing something into the search box.