You should be able to stay airside at ATL (within security) and not be re-screened. When you arrive in Atlanta you need to check the terminal and gate of your departure. I have seen flights to Europe which did not use the International terminal. (It all depends...check the monitors when you arrive in ATL).
Then you take the Plane -Train (underground subway) to your correct departure terminal. A,B,C D or International.
From your arrival gate follow the crowd down stairs to the Plane Train.
Exiting the airport in AMS is a pretty quick and easy process. Should not take long ... after you get any baggage from baggage claim. If you only have carry-on you are ready to go in minutes depending on how many people there are in front of you for the passport check.
Where are you headed in Amsterdam???
If you are going to a hotel there is a good bus shuttle service that will take you door to door (selected hotels). I have used it very easy to use. I think it is called Connex. Google the AMS website to find their booth location. Get directions / suggestions from your hotel.
Other wise the train station is downstairs from the main reception hall. Tickets via a machine and ticket booth.