How can I make a GUI show up on a Players screen when I input the username on another GUI?

I'm trying to make it so there are two GUIs. You put the player's username in the first one, and it should enable another GUI on that player's screen. I'm stuck on how to do this. Could someone please help me?

I suggest you use remote events, Fire to server then fire to username's client. https://developer.roblox.com/en-us/api-reference/function/RemoteEvent/FireClient