ipod shuffle won't show up in itunes mac

If this is a new 4th gen iPod shuffle, make sure the plug on the docking cable is fully inserted into the shuffle's headphones jack, as shown in this document

iPod shuffle (4th generation): Not seen in iTunes - Apple Support

If this is an older shuffle that you've been using for a while, and you are saying it does not appear in iTunes now for some reason, which shuffle model do you have? There are four types. This document shows the models

Identify your iPod model - Apple Support

The blinking orange light indicates the shuffle has a data connection to the Mac. That's good.

I don't know if this worked before with your current Mac and iTunes version... If you are using iTunes 12.x for the first time, how iPods appear in iTunes is different from previous versions. It appears as a small device button on the horizontal bar that goes across the iTunes window. Here's a screenshot of the upper left corner of my iTunes window, with my 2nd gen shuffle as the device button (circled in red).

It does not appear there when connected?

There's a special utility that is only for 1st and 2nd gen shuffle

iPod Reset Utility 1.0.3 for Mac

Since your shuffle appears to have a good connection (blinking light), try downloading and running this utility with your shuffle connected. This utility does the equivalent of a Restore in iTunes, when the shuffle does not appear in iTunes.