Question: My camera came with a USB cable that can be used to connect it to a computer for transferring the photos. What's the difference between that method to using a card reader and what's the preferred way?
Answer: When using the USB cable to connect the camera to your PC, the computer reads the photos while the memory card is still inside the camera. The only "advantage" about it is that you don't need to take the card out of your camera in order to copy the photos. On the other hand, when you connect the camera to your PC with a cable you expose it to the risk of falling and crashing if you or someone else acidentally pull the cable.
Memory card readers are very cheap, easy to install (no driver needed) and thus your camera remains safe where it's supposed to be when not used for taking photos - in its carrying bag. My advice: always use a card reader to copy photos from a memory card.