First of all, you need to install the application on the server.

aptitude install apache2

Then, you need to activate the ssl module (we will reload Apache later):

a2enmod ssl

Next, be sure that Apache listens on the HTTPS port. In the file /etc/apache2/ports.conf, add:

<IfModule mod_ssl.c>
    Listen 443
    NameVirtualHost VOTRE_ADRESSE_IP:443
</IfModule>

…if it is not already present.

So that your certificate can be recognized as having been issued by an approved certification authority, you need to recover the intermediary certificates issued by Gandi : Retrieving the Gandi intermediate certificate

Install your keys/certificates and any necessary intermediary certificates (to form a string) in, for example: /etc/ssl

cp cert-domain.tld.crt /etc/ssl/certs/domain.tld.crt
cp monserveur.key /etc/ssl/private/domain.tld.key
cp GandiXXXSSLCA.pem /etc/ssl/certs/GandiXXXSSLCA.pem

To add a domain name to your secure Apache, create a dedicated website:

vi /etc/apache2/sites-available/000-domain.tld-ssl

…and add the virtualhost of your domain in the following manner:

  <VirtualHost YOUR_IP_ADDRESS:443>

        ServerName www.domain.tld
        ServerAlias domain.tld
        DocumentRoot /var/www/www.domain.tld/
        CustomLog /var/log/apache2/secure_access.log combined

        SSLEngine on
        SSLCertificateFile /etc/ssl/domain.tld.crt
        SSLCertificateKeyFile /etc/ssl/domain.tld.key
        SSLCertificateChainFile /etc/ssl/GandiXXXSSLCA.pem
        SSLVerifyClient None

  </VirtualHost>

Then activate the SSL website by reloading Apache:

a2ensite 000-domain.tld-ssl
/etc/init.d/apache2 reload

Using the following openssl command with your IP address (or the hostname of the server) and the associated port of the service (443 in cas of apache2/SSL) :

openssl s_client -connect ip.ip.ip.ip:port

Or you can use http://www.digicert.com/help/ to visualize the chain on a more graphical way.