There are more Americans claiming German ancestry than any other ethnic group. More than likely, you have at least one German ancestral line that you'd like to learn more about.
Many German immigrants, upon arrival to the new world, took a new surname: the English equivalent of their German names. For example, Mohler became Miller and Schneider became Taylor. These surnames are relatively easy to identify. Other surnames, however, do not have an equivalent in English. These names are transliterated instead of translated. For example, Kurrer becomes Kerr and Dirsch becomes Dearth. [i] German pronunciation is different from English pronunciation, so that is the reason that surname transliterations may have different spellings than their German equivalents. The letters "DT" make a T-sound, and the vowel combinations "AU" and "EU" as "oi." Keep this in mind as you're moving back through your family tree. If names don't make sense, make sure you're pronouncing them the German way.
Because Germany was unified so recently (in the nineteenth century) this can make locating records difficult because there was no central governing body to require all the people to keep records. The key, however, is to utilize church records.
Catholic church records, as you would guess, are all in Latin. Lutheran records, however, can be found in either Latin or German.
Don't forget to check genealogical societies (or online blogs and message boards) that are devoted to German research. You never know what you may find there!
Some other sites that you may find useful are:
Archives in Germany
http://home.bawue.de/~hanacek/info/earchive.htm
German Emigration and Passenger Lists
http://genealogy.about.com/od/german_emigration/
All the civil records that you find (and, as previously mentioned, some church records) are in German. If you don't speak German, you can still conduct genealogical research if you're armed with a few basic German genealogical words:
Christening:Taufe
Burial: Beerdigun,
Wedding: Hochzeit
Birth: Geburten
When you learn a few German words, and some searching techniques, German genealogy becomes easier than ever.
[i] A Genealogical Handbook of German Research, FamilySearch