all of the libraries are located in:
<arduino dir>/hardware/arduino/cores/arduino
for the automatically included files (Arduino.h is the one that's directly included) and
<arduino dir>/libraries
<sketchbook dir>/libraries
for libraries that you #include in your sketch.
Geany doesn't appear to be a compiler --- its website says both that it's an IDE and that its a text editor. It's probably best to just use the avr build of gcc unless you have a good reason not to.