However you won't find it unless your set your region to United States.
The Amazon Appstore is itself an Android application so you are already set, WSA is running already. You could also login on the Amazon Appstore but to date it looks like there are mostly useless games in there. You will only be able to login on the Amazon Appstore using a US based account. From Germany I could create a new account on Amazon.com, then set my post code to anything in the US and that did it.
WSA settings are notably most useful for developers:
enabling developer mode and connecting to WSA using adb. Just run
adb install <path-to-apk>.
Sideload Fulguris on WSA:
adb connect 127.0.0.1:58526 adb install .\Fulguris-v1.8.4-slions-full-download-release.apk
However Google Play store is not currently officially available on WSA. More on that later.
To make it easier to install APK on WSA you could also use Pacman.