Brian and Deborah: When a camera comes with a USB cable to connect it to a computer, the software that also comes with it is usually necessary to make the card inside the camera appear as a "disk" on the desktop — if that happens at all. There may be some cameras that are sufficiently "transparent" to the OS so that cards inside them will appear on the desktop without installing any software — but of the seven or eight different cameras I've used from time to time, none fit that description: all the ones I've used required the installation of proprietary software (provided by the camera's manufacturer) to enable a direct USB connection of camera to computer. In some cases the card inside the camera shows up on the desktop, but in others the photos can only be imported onto the computer from within the manufacturer's proprietary image-browsing application. (After that they can be moved, copied, and edited using other apps.)
The manufacturer's software typically has two parts: (a) an image browser application that often has some editing capabilities, and (b) a USB "shim" or other behind-the-scenes supplement to the OS's standard USB drivers, which facilitates and controls communication between the camera and the computer. You can get along fine without the manufacturer's browser in most cases — any photo editing app will do, once the photos are on your computer. But if you don't have the USB shim, in many cases the camera can't communicate with the Mac, and the card in it doesn't appear on the desktop. If that's your situation, Brian, a card reader is the best solution. It simply eliminates the camera from the equation, enabling the standard USB mass storage drivers in your OS to communicate directly with the memory card.