How to carry List's and Vector3's to other classes? Interfaces don't work?

Ok finally figured it all out! For one my understanding on interfaces was == null;... But I'll explain the answer for anyone else who will have a hard time understanding interfaces as I did :)

In my question code you see:

 IAmSelected selected;
 
 selected = (IAmSelected)gameObject.GetComponent("IAmSelected");
 selected.selectedUnits.Add (ObjectRayHit); //This doesn't work

I had no idea that I was sending that unit back to my List in MainCameraControl! Whatever object you call after the (InterfaceName)objectName <-- is where your telling the interface to send it, obviously the gameObject you want is the one who's Component(script) you're trying to get it into!

Let's take a look at that code after I pulled all my hair out:

 [Raycast logic here]
     GameObject createWaypoint = Instantiate (waypointPrefab, MoveTo, defaultRotation);
     newWaypoint = createWaypoint; //This is needed for certain situations
     foreach (GameObject unit in selectedUnits) {
         IAmSelected carryList = (IAmSelected)newWaypoint.GetComponent("IAmSelected");
         carryList.selectedUnits.Add (unit);
     }

You'll notice 'newWaypoint' the object that MoveToFormation.cs is the Component of, is where I'm telling that "unit" to go. Not back to myself again...

And the mayhem that happened when trying to send the Vector3, or nightmare rather, now looks like this:

 [question related logic]
     foreach (GameObject it in selectedUnits) {
          if (selectedUnits.IndexOf (it) == iterate) {
              IUnitInfo theUnit = (IUnitInfo)it.GetComponent ("IUnitInfo");
              Vector3 pos = new Vector3 ();
              formation = iterate - (calcLine * rowCount);
              if (North == true) {
                 pos.z = (gameObject.transform.position.z - (spacing * rowCount));
                 pos.x = (gameObject.transform.position.x + (spacing * formation)) - calcLine;
                 theUnit.North = true;
             }
             if (East == true) { Etc... }
             if (South == true) {Etc... }
             if (West == true) { Etc... }
             theUnit.spot = pos;
             iterate++;
         } 
     }

A major thanks goes to @Bunny83 for showing me that I needed to call that Vector3 pos... That helped so much, you just don't understand.

And an even more humongous thanks goes to @UnityCoach for helping the less fortunate. He's an awesome guy, with a ton of tutorials on youtube, that probably show this issue. I just somehow didn't notice, lol...

Here's all the code in a nutshell for those who still don't get it, like where I was at several days ago:

 public class MainCameraControl : MonoBehaviour {
 
     //This is the intiating List, so it doesn't get/set
     public List<GameObject> selectedUnits = new List<GameObject>();
     
     Update(){
         [Raycast logic here]
             GameObject createWaypoint = Instantiate (waypointPrefab, MoveTo, defaultRotation);
             newWaypoint = createWaypoint; //This is needed for certain situations
             foreach (GameObject unit in selectedUnits) {
                 IAmSelected carryList = (IAmSelected)newWaypoint.GetComponent("IAmSelected");
                 carryList.selectedUnits.Add (unit);
             }
             
         [Raycast logic here]
             ObjectRayHit = hit.collider.gameObject;
             if(ObjectRayHit.tag == "Units")
                 if (!selectedUnits.Contains (ObjectRayHit))
                     selectedUnits.Add (ObjectRayHit);
     }
     
     private void ListSelected(){
         foreach (GameObject unit in selectedUnits){
             IAmSelected itSelected = (IAmSelected)unit.GetComponent("IAmSelected");
             if(!itSelected.selectedUnits.Contains(unit)){
                 itSelected.AmSelected = true; //This tells unit to display Healthbar
             }
         }    
     }
 }

Then the Interface class

 public interface IAmSelected 
 {
     bool AmSelected {get;set;}
     List<GameObject> selectedUnits { get; set;}
 }
 

The gameObject my units move to class

 public class MoveToFormation : MonoBehaviour, IAmSelected, IUnitInfo {
 
     public bool AmSelected {get;set;}
     public bool North { get; set; }
     public bool East { get; set; }
     public bool South { get; set; } 
     public bool West { get; set; }
     
     [SerializeField] private Vector3 _spot; // this is serializable and editable in the inspector
     public Vector3 spot
     {
         get {return _spot;}
         set
         {
             if (_spot != value)
             {
                 _spot = value;
                 // you can catch when the value has changed, to do things like raise an event
             }
         }
     }
     /// You don't have to write it out like that, you could write it like this
     /// If your code is simple:
     public List<GameObject> selectedUnits {get;set;}
     
     void Update(){
         [question related logic]
             foreach (GameObject it in selectedUnits) {
                 if (selectedUnits.IndexOf (it) == iterate) {
                     IUnitInfo theUnit = (IUnitInfo)it.GetComponent ("IUnitInfo");
                     Vector3 pos = new Vector3 ();
                     formation = iterate - (calcLine * rowCount);
                     if (North == true) {
                         pos.z = (gameObject.transform.position.z - (spacing * rowCount));
                         pos.x = (gameObject.transform.position.x + (spacing * formation)) - calcLine;
                         theUnit.North = true;
                     }
                     if (East == true) { Etc... }
                     if (South == true) {Etc... }
                     if (West == true) { Etc... }
                     theUnit.spot = pos;
                     iterate++;
                 } 
             }
     }
 }

The interface class that carries the Vector3

 public interface IUnitInfo 
 {
     bool North { get; set; }
     bool East { get; set; }
     bool South { get; set; } // You should get the hint where these go
     bool West { get; set; }
 
     Vector3 spot { get; set; }
 } 

And finally the Unit class

 public class UnitsParentScript : MonoBehaviour, IAmSelected, IUnitInfo {
 
     [bools]
     [Vector3 spot]
     [List selectedUnits]
     
     void Update(){
         if (AmSelected == true)
             DisplayHealthbar();
             
         [plenty of question logic]
             moveToFormation = new Vector3 (spot.x, gameObject.transform.position.y, spot.z);
             mainControl.setWaypoint = false;
             float dist = Vector3.Distance (gameObject.transform.position, moveToFormation);
             gameObject.transform.LookAt (moveToFormation); 
             gameObject.transform.position += gameObject.transform.forward * speed * Time.deltaTime;
     }
 }