Cable identification

Hi,

This feels like such a silly question but none the less, what cable is this? I thought it was a USB-A "extender" ie it plugs into the USB port on my Mac and allows me to then plug in a USB key without having to go the the back of the computer every time. But, I can't seem to get the USB to fit in to the cable. After some investigating it seems that there is this triangle shaped piece that is preventing the plugging in. This all leads me to believe that this is not what I origiannnly thought. Thus, I have 2 questions:

1) what is this cable for?

2) what cable can I get to plug into my USB port at the back of the computer which allows me to plug a flash drive in on the opposite side.

Thanks,