How can I add a CONSOLE in my game?

Since I am such a kind person( sarcasm intended ), I'll help you out, even though I am thoroughly annoyed by your constant capitalizing of "CONSOLE."

In my examples, ChatInterface is a table of functions for controlling the chat, and System is basically the player interaction class.

For joining and leaving,

game:service'Players'.playerAdded:connect(
function(Player)--// Whenever a player joins
    Player:waitForChild'PlayerGui';--// Wait for their PlayerGui.
    System.Connect(Player);--// This function will give them a chat GUI once they have loaded into the game, and alert other processes.

    ChatInterface.GlobalAnnounce(
    '[ CONSOLE ]',
    '%s has joined the server.',
    'Really blue',
    Player.Name);
    --// Above function alerts all players a message, which in this case would be the player leaving the game.

end);

game:service'Players'.playerRemoving:connect(
function(Player)--// Whenever a player leaves

    System.Disconnect(Player,'Disconnected');--// This function removes them from the system and forcefully removes their client from the game, incase that they remove()'d their character.( anti-exploit ) If the reason was Exploit, it would ban them.

end);

For earning points,

System.AwardPoints=function(Player,Points)

    local Client=System.Clients[Player.Name] 
    or System.Connect(Player);--// Gets their data in the system.

    Client:SetStats(
    'Points',
    Client:getStats('Points')+Points);--// Changes their Points stat.

    ChatInterface.GlobalAnnounce(
    '[ CONSOLE ]',
    '%s has earned %d points!',
    'New Yeller',
    {Exception=Client.Name},
    Client.Name,
    Points);--// Alerts all but the player that he/she has earned some points.

    ChatInterface.SendMessage(
    '[ CONSOLE ]',
    Client,
    'You have earned %d points!',
    'New Yeller',
    Points);--// Alerts the player that he/she earned some points.

end;

For spamming,

System.OnChatted=function(Player,Message)

    local Client=System.Clients[Player.Name] or System.Connect(Player);
    local Time,Spam=tick();--// Gets the time the message was chatted.
    if(Client.LastSpoke-Time>3)then
        Client.MessagesSpammed=Client.MessagesSpammed+1;
    else
        Client.MessagesSpammed=0;
    end;

    if(Client.MessagesSpammed>=5 and Client.MessagesSpammed<15)then--// They spammed.
            ChatInterface.SendMessage(
            '[ CONSOLE ]',
            Client,
            'Please stop spamming.'..(
                Client.MessagesSpammed<10 and''or 
                ' You have '..15-Client.MessagesSpammed..' chances left.'),
            'Really red');
            Spam=true;
    elseif(Client.MessagesSpammed>=15)then
        System.Disconnect(Client,'Spam');--// alerts all of disconnection by spam.
    end;    
    Client.LastSpoke=Time;
    if(not Spam)then--// Keeps chat free.
        ChatInterface.GlobalChat(
            string.format(
                (Client.IsAdmin and '~%s~'or''),
                Client.Name
            ),
            ChatInterface.FilterString(Message,System:playersUnder13()),--// cuss please, blocks out bad words if under13 accounts ingame.
            ChatInterface.ChatColor(Client.Name)
        );
    end;

end;

You better credit me.

You can always use SetCore (http://wiki.roblox.com/index.php?title=API:Class/StarterGui/SetCore) to create a new chat message with your own custom text and style.

EXAMPLE

game:GetService("StarterGui"):SetCore("ChatMakeSystemMessage", { Text = "[CONSOLE: wravager has left the server]"; })

The code will only run n the client so you may have to make a remote event to call the function in every client.