Getting an SSL certificate from Gandi is a straightforward task.

Just remember to combine two downloaded certificates into one domain.crt file.

Nginx configuration makes every web browser happy.

ssl on;
ssl_certificate     /etc/ssl/domain.crt;
ssl_certificate_key /etc/ssl/domain.key;

ssl_protocols       SSLv3 TLSv1;
ssl_ciphers         HIGH:!ADH:!MD5;
ssl_prefer_server_ciphers on;

To check that certificate is installed correctly just go to Qualys SSL Labs site and perform their test. You will get visual interpretation and quite detailed results.

SSL Server Test