If you want to secure your webserver with ssl (HTTPS) then you have to generate a certificate and get it signed by a trusted CA.
Configure the webserver to use this certificate for the secured site.
If your browser complains about an untrusted connection even it gets the right certificate from the webserver, check if there are intermediate certificates you have to provide too.
If you can't configure your webserver to do this, you can past the intermediate certificate at the beginning of your certificate file (if it's ASCII-Armor) and your browser should recognize it.