How Can I Edit .exe File by Using C/C++? - Code is Posted, I Need Explanation

I got this code in the internet. I mostly understood the code, but i need clarification on some parts. These spot i need somebody to explain it to me:

CreateFile("Application.exe", GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

1. Can you explain what these parameters do?

SetFilePointer(hFile, BYTE_OFFSET, NULL, FILE_BEGIN);

2. I know this points to the offset. Any sugestions on where does this function usually used?

WriteFile(hFile, szBuff, variableSize , &ret, NULL);

3. What is ret return? What is NULL represent?

4. Is patching still used nowadays for updating applications? I never find companies out there giving me patches to update apps i have. I think its done online. Anyhow, any comments will be appreciated.

Please note this code i got in one of the IT websites, i know its not a proper one to use it in a serious application since there are security flaws in it.

#include <windows.h>
#include <stdlib.h>
 
#define variableSize 20
#define BYTE_OFFSET 0x0000FE2A   //assume this is the address of the place we want to edit
 
int main()
{
    LPSTR szBuff = new char[20];   memset(szBuff, 0, 20);
    DWORD ret=0;    
  
    HANDLE hFile = CreateFile("Application.exe", GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    
     if(hFile == INVALID_HANDLE_VALUE){
       printf("\t\tError opening file.\n");
       delete[] szBuff;
       return 0;  
     }
  
    printf("Enter The Change You Want to Make in Application.exe");
    fgets(szBuff, 19, stdin);
  
    if(strcmp(szBuff, " ") == 0 || strlen(szBuff) == 0){
      printf("Error, you did not enter any data\n");
      delete[] szBuff;
      return 0;
    }
  
     SetFilePointer(hFile, BYTE_OFFSET, NULL, FILE_BEGIN);
     WriteFile(hFile, szBuff, variableSize , &ret, NULL); 
    
      CloseHandle(hFile);
      
      delete []szBuff;
    
     printf("Exe Edited :)\n");
     return 0;
}

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