Micro-USB used to be the most common USB port and is still found on many older models. This type of connection allows data to be read without needing a computer. For example, you can connect Flash Drives, or Memory Sticks, directly to your mobile device.
Like USB-A cables, Micro-USB will only go into a port if it's the correct way round. Be careful to match the shape of the port with the Micro-USB cable to avoid causing any damage.