How does this feature work?

Question

C++ / C#

There is a code that has questions

#include <iostream>
#include <fstream>
using namespace std;

void insert(list*& p, char value); 
 
struct list
{
  char symbol;
  list* next;
};

int main()
{
  setlocale(LC_CTYPE, "Russian");
  list* first = nullptr;

  char value;
  cout << "Введите символ ";
  cin >> value;
  insert(first, value);
}

void insert(list*& p, char value) // 
{
  list* newP = new list;
  if (newP != NULL)     //есть ли место?  
  {
    newP->symbol = value;
    newP->next = p;
    p = newP;
  }
  else
    cout << "Операция добавления не выполнена" << endl;
}

1. The insert function takes two parameters, what is the first parameter for? Why pass a pointer to a link as the first parameter to the insert function?
2. list* first = nullptr - It looks like this line creates a pointer to the first element of a singly linked list, why assign emptiness to it?
3. What is going on in this line? list* newP = new list;

Answer 1

Questions should be asked to the developer of this code, because the general answer to all 3 points is because the code is written that way. The background is unknown.

1. The first parameter is a reference to the "head of the list" pointer, the insert function creates a new list element and inserts it at the beginning, so it needs to change the value of pointers to the head
   
2. "C++ implicitly converts nullptr to the appropriate pointer type." Void is assigned because it is empty, and variables should be initialized
   
3. A new list item is created