Just as it sounds a function RETURNS A VALUE
Code:
int blah()
{
  return 1;//THIS FUNCTION RETURNS 1!!!!!!!!!!!
}
float meh()
{
  return 4.5//THIS FUNCTION RETURN 4.5!!!!!!!!!!!
}
int main(void)
{
  weee=blah();//THIS EQUALS 1 BECAUSE blah() RETURNS 1!!!!!!!!!!!!!!!
  yeppers=meh();//THIS EQUALS 4.5 BECAUSE meh() RETURNS 4.5!!!!!!!!!!!!
  return 0;//MAIN RETURNS 0!!!!!!!!
}
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! just for some extra effect