Economy tab → Factories & Buildings: open a category, pick a building, set how many with the count slider and press BUILD. Cost, time, workers needed and estimated income are shown in the box before you commit.
Every production building runs a recipe: it takes daily input goods and turns them into output. A steel mill consumes iron and energy to produce steel. If any input is missing, the line stops — plan the chain end to end.
Buildings have no levels: producing more = building more copies of the same factory. Industrial/Robotic/AI versions unlocked through research do the same job with far fewer workers and much more efficiently.
The small and large siblings of a building are separate definitions: the large one produces more and demands more workers, the small one fits a small economy. Pick the size in the build sheet — you can also upgrade a standing building one size up.
Big-ticket items like ships, aircraft and films run on a multi-day cycle: the inputs go in at the start and the output is delivered on the last day. Days without staff or under repair pause the counter and push delivery back.
Four usual suspects: missing input goods, missing workers (especially university tier), not enough energy/water, or a full warehouse. Tap the building — the stall reason and the needs breakdown are spelled out.
Energy and water are goods too: most buildings consume them to produce. If there is a gap, factories stop in a chain. Build power plants and water facilities; you can also import electricity from a neighbor via a grid link.