How can I check and only show a gui if its the first time a player joined the game?

The title says it all. I wanna know how I can check if its the first time a player plays the game and ONLY shows a GUI if they are.

the first time they join add them to a list then make it so that list doesn't show gui like this

-your function for adding to list maybe called add list-
playeradded:connect("addlist")
x = player.name:find (in my list)
if x then
	gui.disable
else:
	show gui

replace some of the things i wrote because they might not be uppercase or proper syntax