I will assume you mean your are using the Adafruit display and Adafruit_HX8357 library.
I am not sure exactly what you mean by "where are the commands" but perhaps this will help:
Those function calls are used in the examples you have working, ie in "graphicstest" at around line 100.
If you are looking fo the location of the function itself within the library then you need to look in the "Adafruit_HX8357.cpp" file within the library.
I've been quite successful getting graphics drawn, bmp's displayed, buttons working, and custom fonts (with the kind help of rowboteer). I have posted some YouTube videos with free code to draw bar charts, dial displays and a graphing function. Here are the videos, code links are in the description.
I'm using the Adafruit 3.5" display but still the HX 8357 chip.