DebugUtility.HandleErrorIfNullFindObject(playerCharacterController, this);

what this means?,What this means?

DebugUtility.cs is NOT a built-in script in Unity.

I guess you’re working on the official FPS template. Go to Assets/FPS/Scripts/DebugUtility.cs and then you can see this:

    public static void HandleErrorIfNullGetComponent<TO, TS>(Component component, Component source, GameObject onObject)
    {
#if UNITY_EDITOR
        if (component == null)
        {
            Debug.LogError("Error: Component of type " + typeof(TS) + " on GameObject " + source.gameObject.name +
                " expected to find a component of type " + typeof(TO) + " on GameObject " + onObject.name + ", but none were found.");
        }
#endif
    }

Obviously, it’s just a function that shows the error detail to help you debug :).