authoritative server -> the server controls all the entity positions and game rules - the clients just display the results of that, and get to make requests to the server when they want to change things (like asking to move, or firing a weapon, or whatever)
entity interpolation -> clients receive information from the server at (relatively) large time intervals. By interpolating the positions during those intervals, movement can be made to appear smooth even though there isn't a message from the server every frame. Different strategies can be used to ensure movement stays smooth even if a position update is late arriving, and to reduce the lag inherent in interpolating a position over a period of time.
server reconciliation -> if a client is allowed to predict its own position changes (in order to be more responsive to input), by applying the expected results of input to the local entity, sometimes the server responses will contradict that local position because the server knows something the client doesn't.. Reconciliation is the process of fixing that on the client, typically by replaying local predicted input based on the corrected values from the server.
As a relatively new developer, you should get the basic communication working, and forget about interpolation and server reconciliation.