Copy YOUR-DOMAIN.crt to "domain.crt".
Copy YOUR-DOMAIN-issuer.crt to "intermediate.pem".
Copy "domain.crt" and "intermediate.pem" to /etc/ssl/certs/.

scp domain.crt root@foo.com:/etc/ssl/certs/domain.crt
scp intermediate.pem root@foo.com:/etc/ssl/certs/intermediate.pem

Copy "YOUR-DOMAIN.key" /etc/ssl/private/.

scp YOUR-DOMAIN.key root@foo.com:/etc/ssl/private/YOUR-DOMAIN.key

Update your webserver config to use https (examples below).

<VirtualHost _default_:443>
        ServerName foo.com:443
        ServerAlias www.foo.com
        DocumentRoot /var/www/foo.com/html
        SSLEngine on
        SSLCertificateFile    /etc/ssl/certs/domain.crt
        SSLCertificateKeyFile /etc/ssl/private/YOUR-DOMAIN.key
        SSLCertificateChainFile /etc/ssl/certs/intermediate.pem
        SSLProtocol all -SSLv2 -SSLv3
        SSLCipherSuite ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA;
        SSLHonorCipherOrder on
        <Directory /var/www/foo.com/html>
                Options Indexes FollowSymLinks MultiViews
                AllowOverride All
                Order allow,deny
                allow from all
        </Directory>
</VirtualHost>