PC Magazine has a well-written (and unbiased) feature article on the subject:
https://uk.pcmag.com/vpn/117675/do-i-need-a-vpn-at-home
For most people though, a VPN is only really useful when you're using a mobile device and connecting to a public wi-fi point. For example, if you're in McDonald's or Costa, and using their wi-fi, someone else there might have set up a fake wi-fi access point, so that all of your data is routed through it (and available for them to see), rather than the official one that you think your phone/tablet/laptop is connecting. [It should be noted though that, despite reading countless PC magazines and website features, together with law reports, I've never seen a single report of that actually happening].
Other than that, the main advantage of a VPN is that it allows you to fake your IP address (which has absolutely nothing to do with your email address), so that a website that you're trying to access thinks you're in a different location to where you.
For example, my friends in Italy like to watch programmes on BBC iPlayer but the BBC blocks access to iPlayer to IP addresses that are located outside of the UK. By routing their internet traffic through a UK-based VPN server though, they can trick the BBC's server into thinking that they're in the UK, thus enabling them to use iPlayer. Similarly, people in the UK can use a VPN to trick the website of US broadcasters into thinking that they're in the USA, enabling them to watch US TV streaming services here in the UK.