the one from Cakes by Sam? I've had it for quite some time and it came with no instructions. I would like to use it with chocolate fondant for a black and white cake.
if it's one of the glass ones, then you simply roll out your fondant/gumpaste, and then press down with the mold..the edges of the glass will cut the paste...tease it out with a toothpick or such, and there you go.
if it is a silicone mold that has two pieces like the one i have, it confused the heck out of me for a while too. one piece is bigger (bottom half), and then there is a second piece that is just of the design itself. what you do is lay the bottom piece down, drape your paste over it, then place the smaller top layer of the mold over it, making sure to line it up properly. roll a rolling pin over it (slowly, working from center to left, then center to right...the top is bad about sliding around), and essentially what happens is that you now have a double sided lace piece that is really realistic. the kerry vincent wedding cake in my album uses a large lace mold.
hope i've helped a little bit...
The one I have is a large white flexible mold, only one piece.