bdos equ 0005H ; BDOS entry point
start: mvi c,9 ; BDOS function: output string
lxi d,msg$ ; address of msg
call bdos
ret ; return to CCP

msg$: db 'Hello, world!$'
end start

Oh, that's just me saying "Hello World" in assembler. There's a massive list of the program to begin programs over at Wikipedia.