If a player is not in group it makes a instance message into workspace?

Does anyone know how to make it so if someone is not in a certain group, it will put a message that says "Player [playername] is not in group", and it will put it up on screen so people see it?

I'm not exactly sure what you mean, but I have made a script for you that may or may not do what you want... Here you go.

To add your group, get the group ID and replace the 000000 with the new group ID...

g={000000} -- Group ID

function check_groupStatus(player) 
	inGroup = false 
	for i,p in pairs(g) do 
		if player:IsInGroup(p) then 
			inGroup = true 
		end 
	end 
	return inGroup 
end 
game.Players.PlayerAdded:connect(function(player) 
	if not check_groupStatus(player) then 
		local h = Instance.new ("Message")
		h.Parent = game.Workspace
		h.Text = (player.Name.. " is not in the group.") -- A public message that says this player isn't in the group.
		wait(6)
		h:remove () 
	end 
end) 

Hope this helped!