queenseatry , As mayer pointed out in comments there are different models, On some ZTE's the tray closest to the power button is for your network SIM card from your wireless carrier and tray closer to the top is for the micro SD card. Link below will go into more detail about the card slots. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://www.androidheadlines.com/2015/01/android-remove-replace-sim-card-sd-card-zte-grand-x-max-cricket-wireless.html