You can write ascii to the video memory address 0xb8 and it will print to the screen.
VASM
mov ax, 0xb8
mov [ax], 0x48
inc ax
mov [ax], 0x65
inc ax
mov [ax], 0x79
Machine Code
01E0B801 D0E0D048 02E001D0 E0D06502 E001D0E0 D079
VGA Output:
Hey
- mov -- move
- inc -- increment
- mov -- move
- inc -- increment
- db -- define byte
- equ -- assign values to symbols
- cmp -- compare
- jne -- jump if not equal