How can I find out the hometown of my ancestors?

Question:

How can I find out the hometown of my ancestors?

Well, my great grandparents (on my dad side this is) came to America during the great migration I'm assuming. They were German, and I want to find my family back in Deutschland and my hometown where my ancestors once lived, but how would I access records of this info myself? Where do I need to go to get migration records, birth certificates of my great grandparents (which would be in Deutsch), etc?

Additional Details

3 months ago
I know it seems like this should be prior knowledge but I've never had to get my birth certificate, I've had a copy since I got my passport with my parents like 10 years ago.

3 months ago
Great Migration during WW1 or slightly before when all the Irish came over, early 1900's. Could possibly be latter, I have a great great uncle who was in the Kaisers Guard. But definitely around the turn of the century.

Best Answer - Chosen by Asker: 3 months ago
I know it seems like this should be prior knowledge but I've never had to get my birth certificate, I've had a copy since I got my passport with my parents like 10 years ago.