https overview

I. If you're making your own numbers:

You just need a certificate and a private key. These can be encoded in one PEM file. It's easy to make your own PEM file with your own self-signed cert on a vanilla RedHat apache:

cd /etc/httpd/conf/
make host.domain.tld.pem
mv host.domain.tld.pem ssl.crt/

Just be sure to edit ssl.conf to reference the new cert. You can replace:

 SSLCertificateFile /etc/httpd/conf/ssl.crt/server.crt
 SSLCertificateKeyFile /etc/httpd/conf/ssl.key/server.key

With just:

 SSLCertificateFile /etc/httpd/conf/ssl.crt/host.domain.tld.pem

and then restart apache.

II. If you're buying numbers:

You'll probably be asked to:

1. Generate a .key
2. Generate a .csr
3. Give the CSR to the company and get back a .crt

Then have your httpd.conf reference the above respectively with the mod_ssl directives:

1. SSLCertificateKeyFile /usr/local/ssl/private/verisign.key
2. N/A
3. SSLCertificateFile /usr/local/ssl/certs/cert.crt

Once you have your cert you can look it over and see relevant things like how long it will be valid for with:

openssl x509 -noout -text -in cert.crt

Note that you might also run into intermediate certificates. Which Apache can reference with either of the following directives:

 SSLCertificateChainFile /usr/local/ssl/certs/intermediate.crt
 SSLCACertificateFile /usr/local/ssl/certs/intermediate.crt

depending on your version of Apache.