format PE GUI
entry start

include "D:\Program Files (x86)\Fresh\include\win32\win32a.inc"

section ".idata" import data readable
    library kernel, "kernel32.dll"
    library user, "user32.dll"

    import kernel, \
        ExitProcess, "ExitProcess"
    import user, \
        MessageBoxA, "MessageBoxA"

section ".data" data readable writable
    title db "hello.asm", 0
    message db "Hello!", 0

section ".text" code executable readable
start:
    push 0
    push title
    push message
    push 0
    call [MessageBoxA]

    push eax
    call [ExitProcess]
    

    library kernel, "kernel32.dll",\
            user, "user32.dll"    

Why is it declared as MessageBoxA?

format   pe gui
include 'win32ax.inc'
entry    start
;//-----------
.code
start:    invoke   FoXx,0,'Hello Fasm',0,0
          invoke   GoToExit,0
;//-----------
section '.idata'   import data readable
library  kernel32,'kernel32.dll',user32,'user32.dll'
import   kernel32, GoToExit,'ExitProcess'
import     user32, FoXx,'MessageBoxA'