SECTION .data
msg     db      'Hello World!', 0Ah       ; assign msg variable with your message string

SECTION .text
global  _start

_start:

    mov     edx, 13                    ; number of bytes to write - one for each letter plus 0Ah (line feed character)
    mov     ecx, msg                   ; move the memory address of our message string into ecx
    mov     ebx, 1                     ; write to the STDOUT file
    mov     eax, 4                     ; invoke SYS_WRITE (kernel opcode 4)
    int     80h

_call_start:
    jmp _start                         ; jump to the start method