Below are instructions on how to configure a wifi adapter on the Raspberry Pi.

O/S – Raspbian Jessie Lite

1. Login to the RPi  (username:pi password:raspberry)
2. Input the following string, this loads the wifi config file into a text editor;

   sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

3. The config file should already have something like the below in it;

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

4. Add the below lines into the config file, replacing the XXXX’s with your WiFi info;

   network={
             ssid="XXXX"
             psk="XXXX"
   }

5. So, once the new lines have been added, you config file will look like this;

   country=GB
   ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
   update_config=1
                  network={
                           ssid="40RR"
                           psk="xxxxxxxx"
   }

6. To close the editor and save the file, press Ctrl and X then select ‘Y’ and then the ‘Enter’ key.
7. The system should recognize the config change and connect with wifi adapter after a couple of seconds, it it doesnt – restart the Pi using the following command.

sudo reboot