After using the automatically generated creator class to connect to the server, you call methods of the interface. For example,

var
  MyInterface : _Application;
begin
  MyInterface := CoWordApplication.Create;
  MyInterface.DoSomething;

TComApplication AppPtr = CoWordApplication_.Create();
AppPtr->DoSomething;

The interface and creator class are defined in the TypeLibName_TLB unit that is generated automatically when you import a type library.