what is wrong with this online FPS script(not done) ?

I'm trying to make a online Fps so i look at a toturial on youtube (here is the video) i have done just the same has him but when i was going to test it when he did (26:00 in the video) i got a error, can someonehelp me? Here is the script:

 using UnityEngine;
 using System.collections;
 using System. collections.Generic;
 
 public class MultiPlayerManager : MonoBehaviour
 {
     public static MultiPlayerManager instance;
     
     public string PlayerName;
         
     private string MatchName = "";    
     private int MatchMaxusers = 32;
     
     public List <MPPlayer> PlayerList = new List<MPPlayer>(); 
         
     void start()
     {
         instance = this;
     }
     
     public void StartServer(string servername,int maxuser)
     {
         MatchName = servername;
         MatchMaxUsers = maxusers;
         Network.InitializeServer(MatchMaxusers, 2550, false);
         Network.InitializeSecurity();    
     }
     
         void OnServerInitialized()
     {
             Server_PlayerJoinRequest("",Network.player);
     }
     
     
     void OnConnectedToServer()
     {
         NetworkView.RPC("PlayerJoinRequest", RPCMode.Server, "", Network,player);
     }
     
     void OnPlayerDisconnected(NetworkPlayer id)
     {
         NetworkView.RPC("Client_RemovePlayer",RPCMode.All, id);
     }
     
     [RPC]
     void Server_PlayerJoinRequest(string playername, NetworkPlayer view)
     {
         NetworkView.RPC("Client_AddPlayerToList",RPCMode.All, playername, view);
     }
     [RPC]
     void Client_AddPlayerToList(string playername, NetworkPlayer view)
     {
         MPPlayer tempplayer = new MPPlayer();
         tempplayer.playername = playername;
         tempplayer.Playernetwork = view;
         PlayerList.Add(templayer);
     }
     [RPC]
     void Client_RemovePlayer(NetworkPlayer view)
     {
         MPPlayer temppl = null;
         foreach(MPPlayer pl in PlayerList)
         {
             if (pl.PlayerNetwork = view)
         {
                 temppl = pl;
         }
         if(temppl != null)
         {
             PlayerList.Remove(temppl);    
         }
     }
 }
     
     public class MPPlayer
     {
         public string PlayerName="";
         public NetworkPlayer PlayerNetwork;    
     }

that is the scritp, unity says: "assets/Scripts/MultiPlayerManager.cs(2,14): error CS0234: The type or namespace name `collections' does not exist in the namespace `System'. Are you missing an assembly reference?"

i'm new to making games so i do not know what is wrong here.