Discovery GO is a popular streaming service that allows you access to a wide range of content. It allows you to enjoy an episode or watch the entire season of your favorite show or documentary.
However, the service is only available if you sign in with your cable network provider. Besides, your device must have a US-based IP address since the site is geo-restricted. If you try to access it outside the US, you will probably get an error message.
That is why you need a virtual private network (VPN). It encrypts your traffic and passes it through its intermediary servers. When you connect to US servers, it replaces your actual IP address with a US one. Hence, Discovery GO will recognize your access from within the country and let you stream outside the US.