Your Internet Service Provider (ISP) is the one that provides you with the internet at your home. Since your ISP powers your internet, it knows your IP address, geographical location, session time, browsing history, downloading history, and so much more of your private information.
A VPN masks your real online identity (IP and location) and provides you a temporary identity (IP and location). With your real IP disguised, you can conveniently avoid tracking activities commonly done by ISPs as the VPN will route your internet traffic through the server you’re connected to (possibly in another country).