Err...volatile just tells the compiler not to cache the value in a register, that's it. If you don't understand volatile you really, really are not the kind of programmer who should even think about using it.
For a trivial example, see this code:
int f() {
int sum = 0;
for (int i = 0; i < 10; i++) sum += i;
return sum;
}
If you make "sum" volatile, the compiler is forced to do the loop[2].