FortiClient SSL VPN - Use with OpenVPN based Server?

Hi, I am using a OpenVPN based service and would like to connect FortiClient directly to the server I have tried entering the ip adrress of the server and my login / password and it will not connect. There is something about a certificate but on the drop down its blank. I have been sent a certificate but do not know how to import this? Every time I try to connect it says the server is down? Is it possible to use FortiClient in this way (to use with OpenVPN based servers?) and not just connecting to a company network - I like the interface and am keen to use, I have tried looking though all the documentation but can not see either how to import a certificate or to connect to a OpenVPN based server. Any help appreciated, thanks