stuff   db      0cdh, 20h, 0

wat does this do

For which architechture? is that x86 asm?

consult your reference manual

we cant do much with the info you gave us

ya this is x86 asm
can u tell me all machine codes for the instructions.....

i meant where can i find them ......
any link

wat

this is pretty easy...
it's a 3 byte variable which contains a symbol (0x00CD, or a double-line similar to an equals sign used to make box-drawings in console applications), a space, and a null character.

to print this to the screen you would do something like

mov ah,02h
mov dl,0cdh
int 21h

you should do some reading on assembly before you start asking questions like this, like this is pretty basic... learn about segment:offset, the stack, data and code segments, basic syntax, etc. first.