Like the name implies, it shows how cash flows into and out of an organization during the accounting period.  Sources of cash are called cash inflows and the uses of cash are called cash outflows.  All of these are further classified into one of three categories:  financing activities, investing activities, or operating activities.  Again, the names of these categories give you clues:  financing activities are cash transactions associated with providers of the cash (owners and creditors); investing activities are cash transactions spent on productive assets; and operating activities are cash transactions are those from revenue and spent on expenses.