Transport Layer Security is a protocol used to protect communications between endpoints. In web browsing, it underpins HTTPS. Encryption, integrity checks and authentication work together; the exact properties depend on the protocol version and configuration.
A practical example
When you visit an HTTPS service, the browser checks information presented during connection setup. A certificate warning means the browser cannot accept the connection under its normal checks. It is a reason to investigate, not an extra installation step.
What to check
Read the actual warning before taking action. Check the full hostname, device clock and whether you intended to open that service. On an organization-managed device, ask its IT team about its configuration instead of installing an unfamiliar certificate. Keep private account details out of a screenshot you send for help.
What it does not tell you
TLS does not turn every destination into a trustworthy business. A VPN tunnel and a website’s TLS session are also distinct. Do not assume that a normal VPN operator can automatically read all HTTPS message contents just because traffic uses its route.
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.