how to boot raspberry pi headless code example

Example: raspberry pi set wifi headless

crate a file in the root folder of the sd card ("boot") called 
wpa_supplicant.conf
===========contents of file:=================
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=<Insert 2 letter ISO 3166-1 country code here>

network={
 ssid="<Name of your wireless LAN>"
 psk="<Password for your wireless LAN>"
}