MacBook Air says expired certificate
i cannot go to any websites. stats that certificate is expired
[Re-Titled by Moderator]
Usually when you see a message about an expired certificate, it means that the Web site's certificate has expired, and so you can't trust an https:// connection to be secure. ("Secure" in the sense of preventing eavesdropping. A https:// connection to a scam site may be secure against eavesdropping, but that will not prevent the operators of said site from scamming you.). When the Web site's certificate has expired, that's a problem for the site operators to fix, and there's nothing you can do to fix it (other than telling them their site shows up as insecure).
If you are running into problems connecting to most/all Web sites, maybe you have a very old Web browser which doesn't support modern Web security standards very well.
What version of macOS / Mac OS X are you running? What browser are you running on it?