Go to https://duvar.metu.edu.tr and click on the Download Windows 64 bit GlobalProtect agent link. 

Download the application GlobalProtect64.msi and install it. If User Access Control is prompted for elevated privileges, allow.

After the installation, application will autostart and appear on the system tray.

Click on it, and enter duvar.metu.edu.tr as portal address.

Enter your metu usercode and your password as credentials (e.g. eXXXXXX)

It will connect after couple seconds.

For the connection details, follow these steps.