A VPN creates an encrypted connection between your device and a VPN endpoint. While that connection is active, your device’s network traffic is carried through that endpoint.
This can reduce exposure on the network between your device and the VPN endpoint. It does not change how a website or service handles information you intentionally send to it, and it does not make you anonymous by itself.
Before choosing a VPN, read its privacy policy, understand who operates the service, and check whether its explanation matches the product you are using.