Public Wi-Fi and what a VPN changes

A café or airport network is a shared local network. Other people on it, and the operator of the hotspot, can see traffic that is not encrypted. They can also advertise a network with a familiar name.

HTTPS already encrypts the page contents between you and that site. It does not hide the site name from the local network in every case, and it does not hide your IP address from the site. A VPN encrypts the path as far as the VPN server and presents that server's address instead.

Use it when you sign in to mail, work tools, or a bank on a network you do not control. The UK National Cyber Security Centre's note on public Wi-Fi is here: NCSC, using public Wi-Fi safely.

A VPN does not check that the site itself is honest. A phishing page is still a phishing page inside the tunnel.