luminance range
This interactive quiz points to one of the first things you need to master. You need to be able to count fstops. The range of fstops for a subject is known as its luminance range. The luminance range of a subject is one of the starting points for establishing the mechanics of an individual Zone System exposure.

Just to reiterate so that we don't lose sight of the goal, the most important aspect of using the Zone System is not the mechanics of making a good exposure, but the use of a language that allows us to translate subjective mental impressions of a subject onto photographic film and paper. For the mechanics to become second-nature you will need to focus attention on those details. However, make regular mental notes not to over-emphasize technique at the expense of picture idea. As you progress in the Zone System, you might find two aspects of photography leap-frogging each other for which you know better: theory and expression. In general, you will soon reach the point where you have a strong theory of photographic principals. As your strength of theory increases, your ability to see certain expressive potential within a given subject increases also. The second thing, the seeing of expressive potential, is the more important of the two. Photograph from your heart, everytime if possible! That's why you're reading this now isn't it?

Great.