Would work to record audio?

I have a quick question about recording external audio from a Nikon P500. Ok, would I be able to put a micro usb to usb into it and then plug a usb sound card into the usb adapter and then put a mic into the usb sound card?

No.

Get an external sound recorder, it will be much better than the built-in mic in the camera. They start at less than $100.

Record your audio, record your video, in editing you strip the on-camera audio track and replace it with your digital audio from the external device.