How do make a gui that only appears when you join?

How do you make it so that when a player joins, they see a gui pop up?

Well, to avoid this being a request, I will let you know of the events you will use, and you can put together a script yourself.

First, you will need the GUI in Lighting (Or some other place than StarterGui)

Then you would use the PlayerAdded event.

You would then clone the GUI into the Players PlayerGui, and thats it.