Hello. I've made a GUI which shows: The Game is loading...
Now I want that if the game is loaded, the GUI hides, and another one shows. I don't know how to check if the game is loaded and I don't know how to show/hide the GUIs just for the player.
Ok, so I can answer half of your question. I'm not sure about the whole check if the game is loaded thing, to find that you should probably check out the link that Mattscy posted in the comments. In case you missed it, I'll re-post it here: http://wiki.roblox.com/index.php?title=Custom_loading_screen
I do know how to make a Gui show/hide for just the individual player. I'm assuming you have a script but if not I totally get it and I think you can find one, or at least an explanation for one, in the link. But in order to make a Gui appear only to each individual player and not the whole server you would use a PlayerGui. PlayerGui is a type of Gui that affects each player individually instead of affecting the entire server at once.
I hope this answers your question. If you have any questions feel free to ask them in the comments. Good Luck :) Skyraider