Get into a ssh shell as root, preferably on the server you want to make the certificate for. This is two steps, the first will generate a .KEY file. It will generate a passphrase/word. obviously, you would change www.example.com to be for the site you want. Note that when you generate a key/request/certificate, example.com is NOT the same as www.example.com. The www is the host. You can use store.example.com, secure.example.com, although most will want to just use www.example.com, obviously replacing it with your domain name. This will create a file, www.example.com.key that you will need to move later. Ok, first step, make a key:
openssl genrsa -des3 -out www.example.com.key 1024
Next make request certificate, will ask for pass phrase and ask a lot of questions. I think these are case sensitive, so be sure to write down what you use for this exactly, as you will need it later.
openssl req -new -key www.example.com.key -out www.example.com.csr
Now you have two files, www.example.com.key and www.example.com.csr. These will need to be chmod 600 and placed in your httpd config section. On RH/CentOS, this means in /etc/httpd/certs or similar. You will need to point to these in your https configuation of apache. That is all.
Oh, you wanted to actually USE SSL? You will need those files to get a certificate using, the key and request. You cill get a certificate, which is a similar looking text file. Lots of places offer them. The $20 are no less "good" than the $800 ones. You will chmod those to be read by root only and put in the same folder as the request and key. Google it and you can find suppliers of SSL keys, like godaddy and the such.
Google search info only, humans can ignore
How do i make a certificate for ssl?
Generate a request certificate?
How do I set up https?
How do I set up ssl?