Operating expenses are those costs every business has that are not considered directly related to a company's first line of business. Operating costs include sales and marketing, research and development (R&D), and administrative costs.
Investors want to make sure management is doing the best job it can keeping these costs in control. Operating expenses are available on the financial statements that every publicly traded company files with the SEC.
Management also must do a good job turning a profit with its own operations. That means the costs associated with cost of goods sold (COGS), etc. must generate more than those costs. If not, well, the company must be in the wrong line of business. Companies should never be operating at a loss. If a company is operating at a loss exactly why needs to be interpreted by the prospective investor
Operating margins represent the direct relationship between sales revenue and operating income. The operating margin of a firm is the operating income divided by net sales. It shows how much gross profit a company generates before taxes.
Well-managed companies should increase these margins from year to year. The higher these margins are the more profits are available to return to shareholders investing in the company. Operating margins can be a useful tool when comparing two prospective stocks that compete within the same market.
Higher operating margins represent a company in a better position to generate income. For example, a company with a lower operating margin than a competitor in its market will have less flexibility in determining prices. It's competitor with higher profit margins will know this about it's competitor and can "go for the jugular" by slashing prices and stealing market share.