how do ground/air/naval factories work?

[Mrow?~]

how do they work?

[Panterich]

factories produce ground/air/naval units
they work by producing units, check database or wiki

[DC-GS]

After you choose a unit to build, supply the factory with the resources and energy to start building.

[Ninja Zyborg]

select a unit to produce, resource + power in, unit out.

[Witless Wonder]

also to make high tier units you need to feed a basic unit factory into the additive factory, etc. You can use payload conveyors to move units if necessary

[Sauron_the_mad]

factories produce the basic units, those can be upgraded to the next tier with ever bigger reconstructors.
woth mentioning is the part that most T4 units (AFAIK the only exception is the Scepter) are too big for the payload conveyors so the T4 reconstructor must be directly attached to the T5 one.