I guess this is basically for begiiners a tutorial. here is a simple procedure to read string from standard input that is the keyboard

readstring proc near           ;requires si(offset of the string to be stored)
    push ax bx cx dx si di
    mov bx,0b800h              ;row coloumn
    mov es,bx
    mov ax,row
    mov bx,160
    mul bx
    mov di,ax
    mov bx,2
    mov ax,coloumn
    mul bx
    add di,ax
    mov bl,attrf
    mov dl,0
    loop_readstring1:
        mov ah,00
        int 16h
        cmp al,08h
        jne loop_readstring_main
        cmp dl,0
        jle loop_readstring1
        dec dl
        dec di
        mov byte ptr es:[di],bl
        dec di
        mov al,' '
        mov byte ptr es:[di],al
        dec si
        jmp loop_readstring1
      loop_readstring_main:
        cmp al,0dh
        je loop_readstring2
        mov byte ptr cs:[si],al
        mov byte ptr es:[di],al
        cmp password,1
           jne readstring_nopass 
           push ax
           mov al,'*'
           mov byte ptr es:[di],al
           pop ax
        readstring_nopass:
        inc si
        inc di
        inc dl
        mov byte ptr es:[di],bl
        inc di
        jmp loop_readstring1
        loop_readstring2:
        cmp file,1
        jne loop_readstring3
          mov al,0
          mov byte ptr cs:[si],al
          inc si
        loop_readstring3:
          mov al,'$'
          mov byte ptr cs:[si],al
          pop di si cx dx bx ax
    ret
password db 0
file db 0
endp