IF HL is small (<256) then do this

 ld a,l         ; lower 8 bits of hl -> a
 ld (de),a

this means that HL = A if H=0.  ie. the product is less than 256

if you want to store a 16 bit number into a memory address then do the following:

 ld de,xxxx     ; where xxxx = memory address ( a label in the program )
 ld (de),l
 inc de
 ld (de),h