Most of the time when you are using a public network, you are behind some kind of firewall or proxy. One of their purpose is to constrain you to only use certain kind of protocols and consult only a subset of the web.
Nowadays, the most widespread protocol is http and is de facto allowed by third party equipment.
Wstunnel uses the websocket protocol which is compatible with http in order to bypass firewalls and proxies. Wstunnel allows you to tunnel whatever traffic you want and access whatever resources/site you need.