You want to use the libraries provided with the Arduino distribution in your sketch.

This recipe shows you how to use Arduino library functionality in your sketch.

To see the list of available libraries from the IDE menu, click Sketch→Import Library. A list will drop down showing all the available libraries. The first dozen or so are the libraries distributed with Arduino. A horizontal line separates that list from the libraries that you download and install yourself.

Clicking on a library will add that library to the current sketch, by adding the following line to the top of the sketch:

#include <nameOfTheLibrarySelected.h>