How to setup a WLAN manually, if the desktop is not available (its a small widget on the left top otherwise)

Find out the available WLAN networks (there can be more WLAN adapters connected, wlan0 is the first)

sudo iwlist wlan0 scan

Manually add security information for WLAN access.

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

The top of this file has the lines:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

and add for every SSID these lines:

network={
ssid="Your WiFi SSID"
psk="Your WiFi Password"
key_mgmt=WPA-PSK
}

Now wait some seconds and/ortype

ifdown wlan0
ifup wlan0
ifconfig 

to see if an IP has been assigned to WLAN0

If its an hidden SSID this may help

ap_scan=2

just after the line update_config=1

Tip to make WiFi more resilient:

This can be solved with no extra scripts.

In /etc/network/interfaces put:

allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp

The roaming allows the interface to self-heal.