VPN is like an internet-subnet (or even as a tunnel where all the data exchanged on the internet are tunneled) where, however, any data that is exchanged within it's protected, secure and anonymous. In practice, everything is done within this VPN is secure and anonymous. A VPN, then, allows you to navigate in anonymity by hiding your IP address and replacing it with that of the server to which you connect, making it impossible for hackers, third parties or their organizations to monitor you.
Full-fledged creates a VPN that protects your connection and all applications that access the internet: browser, email client, online based applications, etc.
VPN extension ...It depends on the extension, Zenmate for example, in my opinion offer the same level of anonymity but obviously only protect the browser and browsing session.
