Web Service Console Application

Sorry if this has been answered or if its in wrong place.

I have followed the guide here which was really helpful

http://www.c-sharpcorner.com/UploadFile/0c1bb2/consuming-web-service-in-an-console-application/

The problem is that im having is that the API has a login that needs to on before i pull anything off from it.

I'm really new to this but i have managed use the function on API to Authenticate but it seems it doesnt last stayed logged in for the next command, is there anything you could point me at?

Thanks in advance