usb port not found for arduino metro...

trying to upload code for an h-bridge stepper setup.

the L (red led light) is blinking but unsure what that means.

any help would be amazing!

When I try to follow the steps to set-up my metro Mac Setup | Experimenter's Guide for Metro | Adafruit Learning System

and input ls /dev/cu* into terminal - it doesn't recognize my metro plugged into the usb port....