Hello,
I recently purchased an Adafruit Gemma and realized it does not contain a means of serial communication to facilitate programming. I already own an Arduino Uno, so I am wondering if it is possible to use the Arduino Uno as ISP to program the Adafruit Gemma (as long as the Gemma is supplied 3.3V instead of 5V)? If so, would the following guide apply the same way from Arduino Uno to another Uno as to Arduino Uno to Adafruit Gemma: https://www.arduino.cc/en/Tutorial/ArduinoISP? Here is the wiring diagram used in the guide: 
. Thanks!
You program a Gemma with a USB cable. Just follow the online documentation.
In the documentation it also covers what all the pins are for and talks about the "secret" reset pad on the bottom of the board in case you want to use an AVR programmer, such as Arduino as ISP.