A great resource to understand the asynchronous pattern in Flutter is the official codelab available at https://dart.dev/codelabs/async-await.
For Futures, in particular, I also recommend watching the official video at http://y2u.be/OTS-ap9_aXc.
On a more theoretical basis, but extremely important to understand, is the concept of Isolate, which can explain how asynchronous programming works in Dart and Flutter: there's a thorough explanation in the video linked here: http://y2u.be/vl_AaCgudcY.