When you sign in to any one of Amazon's single sign-on apps, you're automatically signed in to all other single sign-on apps installed on your device.
The following Amazon apps currently support a single sign-on experience:
When you first sign in to one of these apps, you're automatically signed in to all other single sign-on apps installed on your device as well. You won't need to enter your e-mail address and password to sign in to each app separately.
The Amazon account e-mail address and password you enter for the first app is associated with all your other single sign-on apps, and is assigned as your primary account.
You can assign different accounts to your other single sign-on apps from the "Welcome" screen by tapping Use a different account for this app. However, if you want to replace your primary account, you first need to sign out from an individual app, which in turn signs you out from all other single sign-on apps.
Note: While you're signed out, you won't be able to access your cloud-based content or apps downloaded from Amazon Appstore. For more information, go to About the Effects of Signing Out from Amazon Apps.