Cant Complete Rougelike 2D tutorial.

using UnityEngine; using System; using System.Collections.Generic; //Allows us to use Lists. using Random = UnityEngine.Random; //Tells Random to use the Unity Engine random number generator.

namespace Completed

{

 public class BoardManager : MonoBehaviour
 {
     // Using Serializable allows us to embed a class with sub properties in the inspector.
     [Serializable]
     public class Count
     {
         public int minimum;             //Minimum value for our Count class.
         public int maximum;             //Maximum value for our Count class.
         
         
         //Assignment constructor.
         public Count (int min, int max)
         {
             minimum = min;
             maximum = max;
         }
     }
     
     
     public int columns = 8;                                         //Number of columns in our game board.
     public int rows = 8;                                            //Number of rows in our game board.
     public Count wallCount = new Count (5, 9);                      //Lower and upper limit for our random number of walls per level.
     public Count foodCount = new Count (1, 5);                      //Lower and upper limit for our random number of food items per level.
     public GameObject exit;                                         //Prefab to spawn for exit.
     public GameObject[] floorTiles;                                 //Array of floor prefabs.
     public GameObject[] wallTiles;                                  //Array of wall prefabs.
     public GameObject[] foodTiles;                                  //Array of food prefabs.
     public GameObject[] enemyTiles;                                 //Array of enemy prefabs.
     public GameObject[] outerWallTiles;                             //Array of outer tile prefabs.
     
     private Transform boardHolder;                                  //A variable to store a reference to the transform of our Board object.
     private List <Vector3> gridPositions = new List <Vector3> ();   //A list of possible locations to place tiles.
     
     
     //Clears our list gridPositions and prepares it to generate a new board.
     void InitialiseList ()
     {
         //Clear our list gridPositions.
         gridPositions.Clear ();
         
         //Loop through x axis (columns).
         for(int x = 1; x < columns-1; x++)
         {
             //Within each column, loop through y axis (rows).
             for(int y = 1; y < rows-1; y++)
             {
                 //At each index add a new Vector3 to our list with the x and y coordinates of that position.
                 gridPositions.Add (new Vector3(x, y, 0f));
             }
         }
     }
     
     
     //Sets up the outer walls and floor (background) of the game board.
     void BoardSetup ()
     {
         //Instantiate Board and set boardHolder to its transform.
         boardHolder = new GameObject ("Board").transform;
         
         //Loop along x axis, starting from -1 (to fill corner) with floor or outerwall edge tiles.
         for(int x = -1; x < columns + 1; x++)
         {
             //Loop along y axis, starting from -1 to place floor or outerwall tiles.
             for(int y = -1; y < rows + 1; y++)
             {
                 //Choose a random tile from our array of floor tile prefabs and prepare to instantiate it.
                 GameObject toInstantiate = floorTiles[Random.Range (0,floorTiles.Length)];
                 
                 //Check if we current position is at board edge, if so choose a random outer wall prefab from our array of outer wall tiles.
                 if(x == -1 || x == columns || y == -1 || y == rows)
                     toInstantiate = outerWallTiles [Random.Range (0, outerWallTiles.Length)];
                 
                 //Instantiate the GameObject instance using the prefab chosen for toInstantiate at the Vector3 corresponding to current grid position in loop, cast it to GameObject.
                 GameObject instance =
                     Instantiate (toInstantiate, new Vector3 (x, y, 0f), Quaternion.identity) as GameObject;
                 
                 //Set the parent of our newly instantiated object instance to boardHolder, this is just organizational to avoid cluttering hierarchy.
                 instance.transform.SetParent (boardHolder);
             }
         }
     }
     
     
     //RandomPosition returns a random position from our list gridPositions.
     Vector3 RandomPosition ()
     {
         //Declare an integer randomIndex, set it's value to a random number between 0 and the count of items in our List gridPositions.
         int randomIndex = Random.Range (0, gridPositions.Count);
         
         //Declare a variable of type Vector3 called randomPosition, set it's value to the entry at randomIndex from our List gridPositions.
         Vector3 randomPosition = gridPositions[randomIndex];
         
         //Remove the entry at randomIndex from the list so that it can't be re-used.
         gridPositions.RemoveAt (randomIndex);
         
         //Return the randomly selected Vector3 position.
         return randomPosition;
     }
     
     
     //LayoutObjectAtRandom accepts an array of game objects to choose from along with a minimum and maximum range for the number of objects to create.
     void LayoutObjectAtRandom (GameObject[] tileArray, int minimum, int maximum)
     {
         //Choose a random number of objects to instantiate within the minimum and maximum limits
         int objectCount = Random.Range (minimum, maximum+1);
         
         //Instantiate objects until the randomly chosen limit objectCount is reached
         for(int i = 0; i < objectCount; i++)
         {
             //Choose a position for randomPosition by getting a random position from our list of available Vector3s stored in gridPosition
             Vector3 randomPosition = RandomPosition();
             
             //Choose a random tile from tileArray and assign it to tileChoice
             GameObject tileChoice = tileArray[Random.Range (0, tileArray.Length)];
             
             //Instantiate tileChoice at the position returned by RandomPosition with no change in rotation
             Instantiate(tileChoice, randomPosition, Quaternion.identity);
         }
     }
     
     
     //SetupScene initializes our level and calls the previous functions to lay out the game board
     public void SetupScene (int level)
     {
         //Creates the outer walls and floor.
         BoardSetup ();
         
         //Reset our list of gridpositions.
         InitialiseList ();
         
         //Instantiate a random number of wall tiles based on minimum and maximum, at randomized positions.
         LayoutObjectAtRandom (wallTiles, wallCount.minimum, wallCount.maximum);
         
         //Instantiate a random number of food tiles based on minimum and maximum, at randomized positions.
         LayoutObjectAtRandom (foodTiles, foodCount.minimum, foodCount.maximum);
         
         //Determine number of enemies based on current level number, based on a logarithmic progression
         int enemyCount = (int)Mathf.Log(level, 2f);
         
         //Instantiate a random number of enemies based on minimum and maximum, at randomized positions.
         LayoutObjectAtRandom (enemyTiles, enemyCount, enemyCount);
         
         //Instantiate the exit tile in the upper right hand corner of our game board
         Instantiate (exit, new Vector3 (columns - 1, rows - 1, 0f), Quaternion.identity);
     }
 }

}

I just copy completed script from this website :https://unity3d.com/learn/tutorials/projects/2d-roguelike/boardmanager?playlist=17150