There is no crafting possible with just a steam generator. Instead, it efficiently converts fuel into electricity. Tapping on a steam generator will bring up a menu with options to remove it or access it.
Accessing a steam generator will display a refueling menu.
When connected electrically to a crafting surface that requires electricity and is in use, a steam generator will begin burning fuel and supplying electricity until either the demand ends or its fuel runs out. As a flywheel that isn't at capacity will always draw power, it may drain a connected steam generator.