Companies that produce electricity, cement, food packages or medicine boxes have a "Manage Production" tab for directors. Here directors can set the total amount of jobs available and the daily wage for workers. Directors will also see a list of currently hired workers, including an ability to fire them. A worker can complete a job once per day, producing a certain amount of product each time. Note that nothing will be produced if the workers don't work, so setting a competitive salary to motivate them is important.
Once resources have been produced, it is the company's task to sell them. You can sell resources either via private trades directly to another company, or by creating a Sell Offer as the production company on The Exchange. It is important to try to balance a good price for your resources based on current market prices and your production costs.