What does "Error for compiling digispark default (16.5 mhz) mean?

Question

Hello so I was trying to make a rubber ducky with digispark default, but when I had all of my sketch written I tried to uploded this error appered:

   Arduino: 1.8.15 (Windows 10), Board: "Digispark (Default - 16.5mhz)"
    core\core.a(main.cpp.o): In function `main':
    C:\Users\Andrea Di Campo\AppData\Local\Arduino15\packages\digistump\hardware\avr\1.6.7\cores\tiny/main.cpp:7: undefined reference to `setup'
    collect2.exe: error: ld returned 1 exit status
    exit status 1
    Error compiling for board Digispark (Default - 16.5mhz).
    This report would have more information with
    "Show verbose output during compilation"
    option enabled in File -> Preferences.

HERE THERE IS ALSO MY SKETCH

// Converted using digiQuack by CedArctic (https://github.com/CedArctic/digiQuack) 

#include "DigiKeyboard.h"



void loop() {
  DigiKeyboard.sendKeyStroke(0);
  DigiKeyboard.delay(5000);
  DigiKeyboard.sendKeyStroke( MOD_GUI_LEFT,KEY_R);
  DigiKeyboard.delay(100);
  DigiKeyboard.print("notepad");
  DigiKeyboard.delay(100);
  DigiKeyboard.sendKeyStroke(KEY_ENTER);
  DigiKeyboard.delay(100);
  DigiKeyboard.print("You have just been DUCKED");
}