Update from ADB option under recovery menu How does one typically use the "Update from ADB" option in the Recovery menu? Do I have to connect the phone via a usb cable to my laptop &amp; provide the necessary update files? 

Where on the laptop do I keep the update files &amp; where will I download these files from? 

In case my phone model helps it is a Moto G 1st edition XT1033.
IDK which Recovery (stock/custom) your device is running because in my device CWM 6.0 for Android 4.2.1 shows "Install zip from sideload" option. Anyhow, I've verified that both options points to same thing i.e. sideloading from PC.

This option will allow you to push a .zip file into the device accompanied by an automated installation of it. For a custom recovery this file can be any app, binary or system update. For a Stock recovery, you'll have to see what it allows to push. (I'm assuming you can only push signed system updates from them.)

The usage is simple. Choose the option in recovery which will show some output like: 


  Send the package to the device with adb sideload &lt;filename&gt;...


Your device (as obvious) has to be connected into PC with ADB drivers installed. Issue the command adb sideload filename.zip where filename.zip is the .zip file you want to sideload. It will show some processing and eventually will install.