I've been looking at a tutorial that shows (http://www.decard.net/article.php?body=tajga&chapter=07) :

mov ax,5
mov bx,5
add bx,[five]
add ax,bx
;here ax contains 15, bx contains 10
five dw 5

Where exactly is it stored? Am I so close I can't see the answer?

add destination, source
Logic: destination <- destination + source
So add ax,bx would be as: addition of ax and bx and result is placed in ax
Like in C: a=a+b

yup, "add ax,bx" is more like "ax += bx", most instructions take paramater in order that first is destination, and second is source, source usually remains unmodofied