I can’t seem to make the mBot appear in the connect->Serial Port menu. Yes, it is on. Yes, it is plugged into the computer via USB cord. It is the MBot with the Arduino IDE software (which is greyed out on my Board menu). I’m confident I am using something incorrect or just need the right download. But I. Need. help. 
using version mBlock 3.4.6
? on how to connect the mBot using USB on Mac
mblockzky
#1
You will need to install the correct driver to get the USB port to show up in the menu. Which version of OS X / macOS are you using? See this thread for a discussion on which driver to use based on your version of OS X / macOS.