Help with x86 assembly(troubles with variables)

Question

I'm trying to make an operativing system in assembly but if I try to work with a numerical variable, the compiler(I use NASM), says that is an error
this is an e example
[BITS 16]
[ORG 0X7C00]
abc dw 0x0
add abc, 2 ; this is the line where the
; compiler detect an error
TIMES 510 - ($ - $) db 0x0
dw 0xAA55

Answer 1

thanks