How do I make "pop - ups"?

Hi! I'm trying to figure out how to script things and lately I've been wanting to make a pop up for the very beginning of my game, and throughout it. Can someone please help me to figure out how?

ex: WHEN left click on object, THEN open sprite "book"

If its even possible to do something like that in Lua... I wish code was that easy... :P

(Sorry, I'm a huge noob when it comes to scripting although I know a bit of basics...)

Well, First you need to know the basics of ScreenGUI's and ImageLabels/ImageButtons. Once you learn the basics of those, edit this code I will give you to what you want your variables to be. :)

local img1 = game.Workspace.StartGUI.Frame.ImageLabel1-- Appointing Variable
local img2 = game.Workspace.StartGUI.Frame.ImageLabel2-- Appointing Variable
local img3 = game.Workspace.StartGUI.Frame.ImageLabel3-- Appointing Variable
local player = game.Players.LocalPlayer -- Appointing Variable

function onPlayerAdded(player)
	While true do
     	 	 img1.Transparency = 0 -- Appointing Transparency
      		 wait(3) -- Appointing Waiting Time
	         img1.Transparency = 1 -- Appointing Transparency
		 wait(300) -- Appointing Waiting Time between pop-ups
		 img2.Transparency = 0 -- Appointing Transparency
     	         wait(3) -- Appointing Waiting Time
		 img2.Transparency = 1 -- Appointing Transparency
		 wait(300) -- Appointing Waiting Time between pop-ups
		 img3.Transparency = 0 -- Appointing Transparency
     	         wait(3) -- Appointing Waiting Time
		 img.Transparency = 1 -- Appointing Transparency
		 wait(300) -- Appointing Waiting Time between pop-ups
	end
end

If this wasn't what you're looking for, Pm me and I can help ya out.