There are three primary connectors for USB3, shown below:
Most everyone knows a USB3 Standard-A cable will work in a USB3 port because they are the same size. But many people may not realize this is also true for the other connectors.
Because the extra pins for USB3 are in a separate part of the connector, you can use a Standard-B USB2 cable in a Standard-B USB3 port, and likewise for the Micro-B cable and port. You won’t get USB3 speeds, but this might be helpful if all you have on hand is a USB2 cable.