Integers are your primary data-type for number storage. int store negative numbers with a technique called 2's complement math. The highest bit, sometimes referred to as the "sign" bit, flags the number as a negative number. The rest of the bits are inverted and 1 is added.
int var = val;
int ledPin = 13;
When variables are made to exceed their maximum capacity they "roll over" back to their minimum capacity, note that this happens in both directions. Example for a 16-bit int:
int x;
x = -32768;
x = x - 1;       // x now contains 32,767 - rolls over in neg. direction

x = 32767;
x = x + 1;       // x now contains -32,768 - rolls over