Insert wifi dongle before booting up your raspberry pi. Using Cli install the wicd-curses:
sudo apt-get install wicd-curses
Wicd is a well-known package to manage wifi networks from any Linux computer. Once installed, you can execute it:
You will be welcomed with a screen showing the available wifi networks. If your network is not showing up, you can try hitting Shift+P and then in the “Wireless interfaces” section type wlan0.