caiocesar use MySQL database & create a login system like "username/password"...
If you don't understand about MySQL (which I don't) there is another simpler way to set up a login system, which took me just 1 hour to understand the whole concept. With the help from rexrainbow (plugin creator) & jomo (tutorial writer), rexrainbow made a login system plugin which is easy to use, it is powered by Parse. Here is the tutorial to it by jomo
https://www.scirra.com/tutorials/1455/p ... rse-plugin
As for your question "How would your game know the information that the player already purchased the product"
In the Parse database plugin that rexrainbow created, there is an option where you can store a player data. So for an example if a player already purchased your One-Time Purchase product to unlock all the other features, levels, characters, etc. You should store the value of that player to "1" for example and then save it to that player database and then update that global variable on the "start of each layout" or "every tick" to the value that is saved to that Username.
And everytime the game runs, if the global variable is "1" (which is the value that is stored in the user database), then the game will unlock all the features, levels, characters, etc.
It's kinda complicated to understand, like I said, one step at a time, if you don't get what I mean, eventually you will in the next few weeks if you keep doing what you're doing.
No problem, I know where you're coming from, 2 and a half months ago, I never thought I could be at the stage of where I am at right now, but because I kept learning and hours of practice doing this everyday, I made it this far to almost releasing my first game on the App Store, its a tough challenge but once I'm done, I'm pretty sure the achievement feeling that I'll get out of this would be beyond the limit.
I'll also write a tutorial on "Uploading your iOS Game using IntelXDK to the App Store" once I'm finished with my project, because most of the tutorials out there for iOS to upload to the app store are outdated and they're not specific enough.