HTTPS carries HTTP over a connection protected by TLS. It protects the communication with the website and supports authentication of that connection. It does not evaluate whether the website’s promises are honest or whether a downloaded file is appropriate to install.
A practical example
A convincing imitation site can use HTTPS for its own domain. Your connection to that imitation can be encrypted while you are still giving information to the wrong organization. Read the hostname as well as the browser’s connection indicator.
What to check
Open sensitive services from a known bookmark or independently confirmed address. If the browser reports a certificate or connection warning, keep the exact message and stop before entering credentials. Check that your device date and time are correct, and contact the service through a separate known route if the warning persists.
What it does not tell you
HTTPS and a VPN protect different parts of a connection. Connecting a VPN is not a reason to ignore a browser warning. It also does not remove a website’s ability to recognize an account that you sign into.
Read the technical reference for the underlying definition. For a connection that is failing now, use the troubleshooting guide. To choose an app, follow the VPN selection worksheet.