A VPN — short for virtual private network - has a number of functions. Primarily, though, it allows you to change your IP address to appear as if you're elsewhere. This means you'll be able to spoof your device into thinking you're either inside or outside the US, giving you the advantage of unblocking and accessing other geo-restricted content.
It's also a security bonus, with other features and components including encryption to take your information and turn it into code, making it unreadable to any prying eyes. Kill switches, split tunneling and the like, also prevent people from seeing what you're doing and allow you to maintain better online anonymity.