When a company’s sales are down, it hasn’t been making money. The word sales refers to income. If a bathing suit company’s sales are low, it should stop making wool bikinis. Sales is also the plural of “sale.”
If a jewelry maker is worried about sales during the year's slow months, he might offer a discount. And when a big company focuses too much on sales, they sometimes lose track of the other aspects of doing business. Stores have big sales. The job or activity of selling things is also known as sales, so you could have a sales job, or even a title like "Director of Sales" or "sales representative."