apt-get install openssl
openssl genrsa -des3 -out server.key 1024
openssl req -new -key server.key -out server.csr

You'll be prompted to enter a password (don't forget it!) as well as fill in company identity information. The most important part is the common name, which is actually the domain you are requesting the certificate for. If you're going without a wildcard certificate you can specify the subdomain ( secure.seanbehan.com ) otherwise it assumes www.seanbehan.com and seanbehan.com to be the same, and will cover both domains www.seanbehan.com and seanbehan.com... however, it will not cover anything.seanbehan.com. Unless you get a wildcard certificate (these cost more money). Enter company details such as country code, state and the rest are pretty self explanatory.

You need to then submit the server.csr file contents to a certificate authority like godaddy, verisign, etc. Grab the contents by opening up the file

 vim server.csr 

After you submit it to them, they then will confirm that everything is correct and then give you the signed certificate back for your use on your server. Unless of course you're faking your company details and are an evil, wicked spammer!

The certificate authority (CA) should give you instructions for installing the cert, as well as other files so that you can serve secure pages w/out any browser troubles!

Just finishing up brewing up some fresh ground comments...