Configure Wireless Networking on the Raspberry Pi 3
 
You’ve then got two options for setting up a wireless connection. It might seem easier to boot into the GUI, but really it’s more straightforward to do it in the command line. You should already have your SSID name. You can scan the available SSID’s by this command, but still need the password
 
sudo iwlist wlan0 scan
This will reveal the SSID in the line “ESSID”. Next, open wpa_supplicant.conf:
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
You’ll need to add or edit the following:

network={
ssid="SSID"
psk="WIFI PASSWORD"
}

Press CTRL+X to exit and save, pressing Y and Enter to confirm. Wireless connectivity should start immediately; if not, use

sudo ifdown wlan0
sudo ifup wlan0

…just restart wireless. You could also simply enter sudo reboot.

It worked on the first try for me!

David K5NX