Confuse about how aurgement works?

[timbean]

I am having a hard time understanding how aurgument work. I understand how one aurgement in a function work. But, when two or more aurgement in a function i get confused. I written 2 simply program to try to understand. The first program is with a function with one aurgement. This is clear and straight foward. The second program contain two aurgement in a function. This i can't understand. Why do i really need to have two aurgument when i can get my value with one aurgument? Can anyone explain how aurgement work?

#include <stdio.h>
#include <stdlib.h>

int square(int y);
 
 int main(void)
{
  int x;
  for(x=1;x<=3;x++){
  
   printf("%d",square(x));
   printf("\n");
 }
 
  system("PAUSE");	
  return 0;
}
 int square(int y)
{ 
     return y*y;
}

This is my second program with two aurgument. I try to make a program that was simply so i can understand.But i don't get how two aurguments works.

#include <stdio.h>
#include <stdlib.h>

int square(int y, int z);
 
 int main(void)
{
  int a=1;
  int b=2;
  
   printf("%d",square(x)+z);
   printf("\n");
 }
 
  system("PAUSE");	
  return 0;
}
 int square(int y, int z)
{ 
     return y*y, z+z;
}