Frankfurt Airport

You will have to go through immigration and get your passport stamped, then proceed to baggage claim. After you get your bags you can exit the :nothing to declare" door, unless your gifts are especially lavish. 5 carat diamond?

On the way home at Frankfurt, you will again go through passport control and get your passport stamped as exiting the Schengen Treaty Zone.

My comment may not be helpful but being prepared is never a bad idea...
I didn't care much for the Frankfort airport. It was my first impression of Germany, as I'd never been there. In my opinion, it was nowhere near as wonderful as what Germany turned out to be. Just some warning not to let the Frankfurt airport cloud your judgement about the beautiful, friendly country.

Frankfurt is a big, sprawling airport. Not overly friendly but efficient. Signage is good -- follow the signs -- and prepare to do some walking. You will go through both immigration (passport control) and customs. Customs is a walk through the Green door with nothing to declare. Should be fairly quick.

As mentioned, yes, you go through Passport Control (Immigration) when landing in Germany, and when you return home. It is separate from Customs, which you encounter after Immigration, and after you pick up any checked luggage. Just follow the signs, which will also be in English. The website is very informative. If you get turned around or confused inside the terminal, look for a Service Point or the Information desk.

I also want to temper the earlier comments about fhe airport. It would have been more informative if the poster had specified what their problems were. Frankfurt, as the major hub for Germany, and in particular Lufthansa and Star Alliance, is big and sprawling, with several different concourses. It is modern and efficient. I'm not sure many airports in the world qualify as "wonderful ", but that may depend on how one defines the term. Well, except maybe Changi, but I digress. It's certainly not as big and busy as LHR, CDG, or AMS. Have a great trip!

I wish that I had paid more attention to remarks like triplet's years ago before my first transfers at FRA !

Paul Theroux and our own Rick like to say that you can't get a real feel for a country unless you cross into it overland, and lord if you don't hope that is true when you go through FRA airport. Earlier decor featured huge unfinished steel (maybe it was aluminium?) klieg lights and kitschy food carts selling stale pretzels and watery coffee. It is not quite as bad as that now, but for travelers connecting to France or Italy your anticipation is whetted by the contrast. You know something is amiss when people are choosing to wait in line for a Brioche Doree or a Sbarro.

The one positive thing I will mention is that if there is some small German item you favor there might be versions of it in the shops at FRA that you won't come across in the USA. I have in mind particularly Lamy pens or dark licorice. But in those cases they will be priced better in MUC than in FRA for some reason. Regional tax rates, maybe?

I was at the Frankfurt Airport last week, and was pleasantly surprised by how it was much more efficient than when I had gone through 2 years ago, and had to wait on the security line for 35 minutes, even though we were considered "priority" flying business class. There was no wait this time, and even though it was stated on the FRA website that liquids would need to be separated, I was told I did not need to show my liquids bag, as the security guard pointed to their new equipment.
For your return flight, if you are flying on 2 different airlines, I would check beforehand if you will land in Terminal 1 from Hamburg, and then need to go to Terminal 2 for your flight to the U.S. If so, there is an easy shuttle bus that goes between terminals, and takes about 10 minutes. Will your luggage be checked all the way through, or will you need time to pick up your luggage after the Hamburg flight, and then re-check to the U.S.? I would research this so you know what to expect, and how much time you will need between flights. I hope you have a great time. Other than a dishonest taxi driver in Baden-Baden, I have never had a bad experience when visiting Germany.

tripletblessings, a little personal color on the subject is always appreciated.

Frankfurt Airport is massive but manageable. We much prefer it, for example, to Heathrow Airport.

Or LaGuardia, or O'Hare, or LAX...

But not as good as DFW and IAH

I like DFW. They have a great USO and good food. If I have to hang around an airport that's one I like. Also St Louis. Denver. Minn/St Paul, even El Paso. I can forgive a lot if they have good food and booze. Helps if the help is attractive too.