As previously mentioned, German wines are among the most clearly defined wines in the world, and yet they can be seem confusing. A brief run-down of the classes of wine you are most likely to encounter is in order. First off all German wine is broken down into three categories. Deutscher Wein at the bottom, a category you are unlikely to encounter. Then comes Landwein, a wine from a specific region. In general these are dry (trocken in German) or off-dry (halbtrocken). It is somewhat unlikely that you will encounter these wines but not impossible. Fortunately there is not much additional information you might need to decypher one of their labels.
That leaves the Qualitätsweine mit Prädikat, the highest level of wine quality that is also subject to additional designations. While space prevents me from going into too much detail regarding the additional levels of labellling that can help guide the consumer I would suggest looking the the guide to Deciphering German wine labels
for a brief rundown of the basics terminolgy used to identify the potential sweetness levels of most German wines. This seems to be one of the areas which people find most confusing when it comes to German wines.