Operating activities include the production, sales, and delivery of the company's product as well as collecting payment from its customers. This could include purchasing raw materials, building inventory, advertising, and shipping the product.
Investing activities include purchases or sales of an asset (assets can be land, building, equipment, marketable securities, etc.), loans made to suppliers or received from customers, payments related to mergers and acquisitions, and dividends received.
Financing activities include the inflow of cash from investors, as well as the outflow of cash to shareholders as dividends as the company generates income. Other activities which impact the long-term liabilities and equity of the company are also listed in the financing activities.