How can I make navfn plan independent of the rest of the navigation stack packages?

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I am using a launch file which has the following three nodes: 1) map_server: to upload map parameters in .yaml format 2) rviz: which provides the start and goald points (2D pose estimate and 2D Nav Goal) 3) navfn_node: the global planner.

when I roslaunch this file, navfn_node does not subscribe to the start and goal points. I have tried to go through the ROS literature but it is very confusing. My question is, am I supposed to use the Base_Global_Planner instead of navfn in order to use global planner independently? If so, which file in navigation stack would serve as the node, and also does it already subscribe to the start and goal points. If I can directly use navfn, how which topic do I subscribe to and how?