Vim has this awesome feature for referring to the documentation of a command or functions.
To get the documentation or the man page of a command or a function from within vim, Go to your command or function and press
Shift + K
To Check for this yourself :
Open your Vim editor with some file
Type in some commands or functions
Move your Vim cursor to the 'scanf' and press 'Shift+K'
You will be presented with this awesome manPage(documentation) for the scanf function.
This can be carried out with any commands or functions.
Shift+K basically presents you with the documentation associated with the command in your file.
How cool is that ? :)