Depending on the food being made and type they will likely have a sort of silk screen printing concept going where one print head will "paint" or "print" it's components into place in the first microscopically thin layer, then another print head will fill in it's own ingredients.
They may have them working simultaneously if they can figure out how to do it without one print head running into another. The food printing is done via a CAD designed blueprint (computer aided drafting blueprint), or design that is fed into the program.
The computer can then slice the design into layers and print it out one layer at a time fusing the last to the next and in this case- cooking the ingredients together.
It may need to cook them but not all the way to allow for the sections not to over cook layers. It's not exactly like melting metals or plastics together when it comes to food. More than likely the cooking part may happen separately. A cake could essentially be created into a thick batter that can stand on it's own while printed, you'd cook that portion, let it cool, then put it back in the printer to automate painting and frosting the cake- even adding cool designs in 3D.
Imagine having one of these in your home and simply putting your recipe into the computer formatted based on a specific standards. To take it one step further, imagine instead of cooking that recipe you like from the site- you download a file that plugs into your food printer and it simply makes it. You'd purchase temporary use recipe aps!
Your only responsibility will be to make sure you have certain ingredients for it in the cartridge. Likely you will be able to swap out cartridges and they will sell you the filler ingredients in a certain format for the machine to use.The likelihood is that the recipe downloads would be sent directly to the machine itself which would be jacked into your wi-fi internet.
Some sort of anti-piracy concept would have to be created so your machine can use it but you can't duplicate or store/save the recipe (unless you pay for a permanent version which is unlikely to be available at first).
They may have an LCD screen with a limited internet access screen that connects via broadband to their site or service and you'd just say, wow I want to get this recipe or that. You may be able to rent the recipe like you rent videos online- it would expire after the food was prepared or you could permanently buy the recipe. How cool would that be. Since the machine would only need to view the schematic it could be encrypted and likely would display what's in the recipe so you know if you want it or are allergic to anything in it.
It's also likely that the basic recipes this device will make will not be elaborate at first but will evolve in time as any technology does.
One more innovation of food this device promises is the ability to "shape" your food. For example broccoli could be minced and printed into transformer shapes even sweetened with fruit juices (healthier) so kids don't realize they are eating vegetables at all! How about some Tetris vegetables?