what is << in vim code example

Example: indent vim

Be in visual mode (v).
Use the > command. To indent five lines, 5>>. 
To mark a block of lines and indent it, Vjj> to indent three lines (Vim only). 
To indent a curly-braces block, put your cursor 
on one of the curly braces and use >% or from 
anywhere inside block use >iB.

If you’re copying blocks of text around and need to 
align the indent of a block in its new location, use 
]p instead of just p. This aligns the pasted block with
the surrounding text.