How select a player for give at him a variable?

What I want to do is give each player a variable to give them different objects to each of them but I want to know how to choose the player number 1, number 2, number 3 etc.

You don't know how to iterate all players? It's fairly easy.

You need to use the GetPlayers() function of the Players service, then use it in a for loop, like so:

for i,plr in pairs(game.Players:GetPlayers()) do
	--do stuff
	--plr is the player
end

If you want to store a variable per player, you have two options:

1. Use tables

Make a dictionairy table of tables with data, in which the keys are the player names, add values to it when a player joins with PlayerAdded event

local data = {}

game.Players.PlayerAdded:Connect(function(plr)
	--load data if necessary
	data[plr.Name] = {Cash = 0}
end)

game.Players.PlayerRemoving:Connect(function(plr)
	--save data if necessary
	data[plr.Name] = nil
end)

1. Use Values

You can use values instances such as StringValue and parent them to the player when they join

game.Players.PlayerAdded:Connect(function(plr)
	local cash = Instance.new("NumberValue", plr)
	cash.Name = "Cash"
	cash.Value = 0
end)

while true do
	local players = game.Players:GetChildren()
	local radplr = math.random(1, #players)
	print(radplr .. " chosen")
end