The Two Factor Authentication (2FA) works as an app on your smartphone ("Google Authenticator" or "Authy" for Android and Apple’s iOS and "Authenticator+" for Windows Phone).
If you already used it, you should find an entry for Bitpanda. The number there changes every 30 seconds. This is the actual 2FA-code. You will be required to enter it at login in a second step after you entered your email, password and the captcha.
If you have not used 2FA for Bitpanda before you have to configure it first. In order to do so log in to your Bitpanda account and navigate to Security. Here you will find the QR-Code that you have to scan with your 2FA-app. To complete the setup, you must enter and confirm the code on the website that is now shown in the app.
If your Bitpanda 2FA entry doesn't work, you could try to get it fixed by navigating into the app-settings and synchronising the time. Your time and date settings need to be up to date for your 2FA codes to work.