I'm making a continue gui where If a player reaches a certain place in another game lets say "Night 1" (that's made by me) and quits the game then if he plays the main game (where the continue gui is) and clicks continue he gets teleported to "Night 1" via TeleportService
or whatever game he had reached that certain place in. Basically can you detect if a player has reached a certain point in a game? (that certain point can be anything a part or anything)
Any help is appreciated.
By game, I'm going to assume you're talking about "places". (A game can hold several "places" inside it).
Within each "place" you have, you'll want to create some sort of data storage system that can be accessed by all places within the game and saves what place, level, area, etc, that the player is currently on. This could be done by creating a data store with the key being the player's UserId and the value being the place Id of the place he last played in. Then in the game's start place (where the 'continue' GUI will be), you could have that GUI access that same data store and teleport the player to whatever place id and location is saved within their data store.
Here are the links to the Roblox Wiki pages relevant to the goal you want to accomplish. I highly recommend completely reading and soaking in everything these pages have to say. It'll make your task very do-able, and you will learn a good deal.
I hope this helps!