Vim editor, how can I save a file in other directory - Ask Ubuntu

i'm new in world of ubuntu , vim editor.
question is: how can save file on localhost using vim?
when use command :w save file, where? , how can change file location /var/www/?

you can enter :pwd display current working directory. file saved if enter :w filename. can change working directory :cd path/to/new/directory. or can enter full path location want save file write command, e.g., :w /var/www/filename.