At the command prompt type
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
This will load a basic text editor with the wifi configuration file.
You will just need to add a new “section” to the file for your network or modify an existing one.
e.g. Say that your SSID is “salmagundi” and it uses WPA2 security with a wifi password of “n0beef” you would add the following lines
To save this press <Ctrl> X then press Y and finally press <ENTER>.
At this point if you reboot your device it should then connect to your WiFi.
Now remove the Ethernet Cable.
During boot up you should see the WiFi dongle’s activity light start blinking (rapidly) to indicate it has established a connection to your wifi.