I want to make a lag testing game so to say but my script is not working ????

the problem is at line 13 (the one with a comment) I don't know how to make it say "parts = number(the number of parts I spawned)"

local g = "Times"
local number = 1
local text = game.StarterGui.ScreenGui.TextLabel

while number < 50 do
	Instance.new("Part",workspace)
	print(g,number)
	wait(0.2)
	number = number+1	
end

while 3 ==3 do
	text.Text = "parts =",number --here
end

The reason you got an error is because the value is a number value and not a string value. Use tostring(value here) to convert it.

New Code:

local g = "Times"
local number = 1
local text = game.StarterGui.ScreenGui.TextLabel

while number < 50 do
    Instance.new("Part",workspace)
    print(g,number)
    wait(0.2)
    number = number+1   
end

while 3 ==3 do
    text.Text = "parts =",tostring(number) --use tostring
end

Good luck on that lag test!

Add a .. to any string to add a part of the code to it.

local g = "Times"
local number = 1
local text = game.StarterGui.ScreenGui.TextLabel

while number < 50 do
    Instance.new("Part",workspace)
    print(g,number)
    wait(0.2)
    number = number+1   
end

while wait() do -- use this instead because while 3 == 3 is pretty much while true do and you need a wait to stop your game from crashing.
    text.Text = "parts = " .. number
end

Not sure if this is still needed but i've re-wrote your script to include a percent bar on your text button. The code is as follows:

local STGui = game:GetService("StarterGui")
local Screen = STGui.ScreenGui

local PerBar_Props = {
	ClassName = "Frame",
	Parent = Screen,
	Name = "Bar",
	BackgroundColor3 = Color3.fromRGB(81, 38, 255),
	BackgroundTransparency = 0.3,
	Position = UDim2.new(0,0,0,0),
	Size = UDim2.new(0,0,1,0),
	ZIndex = 1,
	Visible = false,
}  


function createElement(Props)
	local ClassName = Props.ClassName
	--print(Props.Name,ClassName)
	local Obj = Instance.new(ClassName) 
	for k,v in pairs(Props) do
		if(k ~= "ClassName") then
			Obj[k] = v
		end
	end
	return Obj
end
local text = game.StarterGui.ScreenGui.TextLabel
text.TextStrokeColor3 = text.BackgroundColor3
text.TextStrokeTransparency = 0

PerBar_Props.Parent = text
local PBar = createElement(PerBar_Props)

--// change this value to change how many parts you want to load!
local howmany = 500

local Part_Props = {
	ClassName = "Part",
	Parent = workspace,
	Position = Vector3.new(0,0.5,0),
	Name = "Part"
}

for i=1,howmany do
	local P = createElement(Part_Props)
	wait(0.2)
	text.Text = "parts ="..tostring(i)
	local Percent = (i/howmany)
	--print(Percent)
	PBar.Visible = true
	PBar.Size = UDim2.new(Percent,0,1,0)
end

The createElement() function is just a function that would create an object int this instance i create a frame that matches your textLabel Size and position then i also use it to create the parts. To target a property of your part just include the value inside the table Part_Props

Something like:

local Part_Props = {
	ClassName = "Part",
	--// new entries!
	Anchored = true,
	Color = Color3.fromRGB(0,255,255),
	--//
	Parent = workspace,
	Position = Vector3.new(0,0.5,0),
	Name = "Part"
}

Then re-run the script to see the changes. Though make sure you match the propety exactly otherwise the script will throw an error

Example:

local Part_Props = {
	ClassName = "Part",
	Parent = workspace,
	color = Color3.fromRGB(0,255,255), -- this wont work the letter c MUST be a Capital!
	somethingelse = "blah", 			-- this will not work either as somethingelse isnt a property of a Part!
	Position = Vector3.new(0,0.5,0),
	Name = "Part"
}

Hope this helps! :)