Please be more specific: What do you mean by "the engine to make Fangames"? Do you mean a game development kit such as Game Maker, Clickteam Fusion, Construct, or Godot? Or do you mean one of the popular engines used for making fangames with those tools - like the engines made by Gatete or Hello?
Try downloading one of the engines and playing around with it. You'll get the hang of it pretty quickly, but if you have questions about how to do specific things (like creating a new room or editing an object), we'll be able to help you.