create a file in the root folder of the sd card ("boot") called
wpa_supplicant.conf
add scan_ssid=1 if connecting to hidden network
===========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>"
}