Unless you are lucky enough to yourself be a German immigrant or have a close ancestor whom you knew as one, you have to be quite creative in finding places of location and origin in the old country. Tersely put, Germany has only been a country like the US since the 1870s. Of course people have lived there for millennia, but records are often kept at a very local level. Therefore you need to find the exact place of your German ancestor. A specific location will help you find church records and other sources of genealogical information across the sea. This is not as easy as it seems. Where do you look here in America?
Sometimes it is as easy as looking in old German church records. While immigrants’ children were born in the USA, the parents themselves were often married in America. And when they died, even after being in the USA for 60 years or more, the church records may show the place of origin. That’s how and where I found my own ancestors when I started. The marriages showed the exact place of birth in Germany. I am on a committee which has digitized and put online 150, 000 pages of local church records, and sure enough there are the locations and places of origin for thousand of Germans married in this town in the mid to late 1800s.
Then again, spelling errors can even be found in foreign languages. Sometimes they are understandable, and other times you really have to double-check. Is it really Orrosphe or is it Oberosphe? Schaafheim, Schafheim, or Schopfheim? Niedersheim or Niederschaeffolsheim (that last one was a misnomer that I determined was wrong when the people I sought were not quite right. Close, but not right.) And a personal visit to the shorter named town showed no evidence of my relatives, since they were from the longer named town.
Another place to look is civil records. Many times a place kept marriage licenses, and those may also give the place or origin. So might wills filed in a probate court. I know of a case where someone went back to Germany without selling a property. When the co-owner went to sell years later after that man had died, his will - in German and from Germany - is filed in the local probate court. It gave his children and grandchildren along with where they lived. This was actually verified by an elderly relative who came here to visit.
Early newspapers may have information printed in German or English. Oftentimes the place of origin is given in those. Libraries and archives may well have them, although it is unlikely that they have been indexed.
Passenger lists are another place to look. Be advised though, that spelling is a rather cavalier pastime. In one case with which I am familiar the same town is spelled 9 different ways for nine different people. Or take the example of Ujverbasz, Verbasz, Vrbas, Werbass, and N. Urbai. They are all the same town (Vrbas or Neu-Werbass) near Novi Sad in present day Serbia. If one knows where the people came from, it makes sense. But none of those places is right. Sometimes the compilers of “Immigrants from (such and such a place)” were very accurate, and sometimes not. Having a province is helpful, but you need the actual town to go further. The Germans to America series is nice to have - but I got really frustrated with the misspellings or lack of information in it.
And remember that Germans can be from France (Alsace-Lorraine, etc), Scandinavia (Denmark), Poland (which was partitioned), Austria, Switzerland, Northern Italy, the old Austro-Hungarian Empire which turned into Yugoslavia and the countries which have formed from that area; and even Russia.