C++ :: Return A Pointer To The Character At The Index Given

I need understanding the logic behind this function. The function is supposed to "Return a pointer to the character at the index given" . For example, what exactly are we declaring at "(char * const c, int index)"? where does "index" come from or equal to in the body of the function?

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char * GetValueAtIndex(char * const c, int index)
{
int i = 0;
char *p = c;
while (i++ != index)
p++;
return p;
}