It is registered in the main mod class.
public GuiHandlerRailsCraftingTable guiHandlerRailsCraftingTable = new GuiHandlerRailsCraftingTable();
NetworkRegistry.INSTANCE.registerGuiHandler(this, guiHandlerRailsCraftingTable);
Also I saw this "player.openGui(TutorialMain.instance, 3, world, (int) player.posX, (int) player.posY, (int) player.posZ);"
I don't have anything like that. Should I have it and where do I have to put it?