Your certificate is not trusted for several reasons the most important of which is that your server signed the certificate. Why should browsers available to people all over the world trust your server to issue an SSL certificate? There are Trusted Root Certificate Authorities. Those are CAs that a web browser trusts to issue SSL certificates. The list varies by browser (and version of browser). I would encourage you to seek out some tutorials on SSL and how Certificates (and Trusted Root Certificate Authorities) work.