Okay, 2 step stamping is actually EASIER than most techniques (in my opinion).
First, you need TWO ink colors that coordinate somewhat (doesn't have to be similar color, just not contrasting). One must be lighter than the other (significantly so).
Second, you need to buy CLEAR stamps that are INTENDED for 2-step stamping. If you don't have 2 images to work with, it, well, won't work !
Okay, got your inks and stamps handy??
Take the FULLER (first) image (in my example it is the full solid flower) with the LIGHTER ink. Stamp it.
Then, take the OTHER (second) image (in my example it's the "shoots" coming out from the center) with the DARKER ink. LINE it up. stamp it.
The END! It really is that easy. As I've perused blogs recently, I have even found THREE set stamps that look pretty cool.