How to make a random player picker and teleport them to a block?

Hello. I have a Scripting question. So, I am trying to make a game where basically a player gets teleported on a stage for 45 seconds, and then after that 45 seconds, that player gets teleported back to spawn. So basically, a random player gets teleported to a part for a specific amount of time (the stage), and after that amount of seconds, they get teleported back to another part (which is the spawn) Help would be appreciated. If you don't understand but want to help, please ask so.

So far, this is what I have put to select a random player:

wait(5)
local num = math.random(1, #game.Players:GetChildren())
print(game.Players:GetChildren()[num])
local player

Then, I have tried making it so it teleports the player:

wait(5)
local num = math.random(1, #game.Players:GetChildren())
print(game.Players:GetChildren()[num])
local player
player.CFrame = CFrame.new(11.667, 23.652, 95.261) -- position
player = nil

The problem is that it doesn't teleport the player and an error says "attempt to index nil with 'CFrame' ". Please help me fix it so it actually teleports the player and make it so it after 45 seconds it teleports that player back to another block (the spawn)

You gotta set the player to the random player

wait(5)
local num = math.random(1, #game.Players:GetChildren())
print(game.Players:GetChildren()[num]).Character.HumanoidRootPart
local player = game.Players:GetChildren()[num]
player.CFrame = CFrame.new(Vector3.new(11.667, 23.652, 95.261)) -- position
player = nil
-- teleporting to spawn
wait(45)
player.CFrame = CFrame.new(Vector3.new(0,0,0)) -- or whatever the position of the spawn is. You can also get the position of the spawn part to do this.

It's because you didn't set the player variable, just as what @JustinWe12 said.

Let's say you have Part named StagePart in Workspace and a SpawnLocation where all player spawns.

To teleport the Player to StagePart, you don't need to set Player.CFrame because the Player Instance doesn't have a CFrame. Instead, get the Player's character model using Player.Character and use its CFrame using Character:GetPivot().

To teleport the Player back to spawn, we simply do Player:LoadCharacter() because it respawns the player. When a Player respawns it will automatically teleport them to a SpawnLocation.

Also we should make a BindableEvent that will detect if Player left or died.

The script should look like this:

local Players = game:GetService("Player")
local StagePart = workspace.StagePart
local Spawn = workspace.SpawnLocation

local bindableEvent = Instance.new("BindableEvent")

function tpRandomToStage()
	task.wait(5) -- task.wait() is slightly faster than wait()
	
	local allPlayers = Players:GetPlayers() -- basically :GetChildren() but only choose Players
	local randomNumber = Random.new(os.time()):NextInteger(1, #allPlayers)
	local randomPlayer = allPlayers[randomNumber]
	local randomCharacter = randomPlayer.Character or randomPlayer.CharacterAdded:Wait()
	local randomHumanoid = randomCharacter:FindFirstChildWhichIsA("Humanoid")
	
	randomHumanoid.Died:Connect(function() -- when the player died
		bindableEvent:Fire()
	end)
	
	randomPlayer.CharacterAdded:Connect(function() -- when the player respawns
		bindableEvent:Fire()
	end)
	
	Players.PlayerRemoving:Connect(function(player) -- when a player leaves
		if player == randomPlayer then -- if the player leaving is the same as the player on the stage
			bindableEvent:Fire()
		end
	end)
	
	bindableEvent.Event:Connect(function()
		return -- stops/breaks the whole function
	end)

	-- PivotTo and GetPivot are both CFrame
	randomCharacter:PivotTo(StagePart:GetPivot()) -- teleports the player
	task.wait(45)
	randomPlayer:LoadCharacter() -- respawns the player and teleports back to spawn
end

tpRandomToStage()