As the name implies, Lava Fabricator produces Lava when supplied with either EU or MJ. It can take in a max of 1000 EU/t or 400 MJ/t. It requires 50,000 EU or 20,000 MJ to fill up its internal tank of 1000 mB (1 bucket worth). A lava fabricator will output lava automatically; it does NOT need a wooden waterproof pipe for example.
One possible setup is to place a stirling engine next to the lava fabricator, then place a endertank above it. Effectively it converts coal power into lava power if you then use the lava in a magmatic engine or geothermal generator.