Int 21 function 02H

Here is  simple prorgam to display a character. 
    mov ah,2
    mov dl,'A'
    int 21h



 
Display a string of characters. there are better methods like write directly to memory,  check the main 8086 area for the same.

    msg     db  1,2,3,"Hello World This is a test",13,10,"$"
    len     equ $-msg

            mov si, offset msg
            mov cx, len
            
    do:     mov dl, [si]

    	

            mov ah, 2     ;Display Character
            int 21h

    	21-09.gif (1068 bytes)

            inc si
            loop do