vim /etc/hosts: open the hosts file.
<C-g>: echo the status of the file, in this case : [RO]
Go: add a blank line at the end of the file. Vim echoes a message that reads 'W10: Warning: Changing a readonly file.', after showing that message, Vim proceeds by making the change anyway.
Note: Vim won't prevent us from making changes to a readonly buffer, but it will prevent us from saving the changes to disk.
%: expands to represent the path of the current buffer, in this case: /etc/hoststee /etc/hosts > /dev/null: receives the contents of the buffer as standard input, using it to overwrite the contents of the /etc/hosts file.