Web Service Certificates Authentication

Hi, I'm having problem invoking a WebService outside of the network where I work, I have read some article about invoking it using WebService Enhancment 3.0 with certificates but I really don't know how to do that. I'm going to use two Web Service, one in a server inside the network, this one is going to retrieve data from the database and sending to the server outside the network, the other one is going to receive it and uploaded in a Website. The thing is what exacly is the code that I have to use to invoke the WebService and pass the certificate and what code to received. I have to do something else? Thank You!! Javier From Puerto Rico.