I'm writing an android program which must interact with google documents, so I have watched this sample, but it uses an AuthSub token. How can I get an AuthSub Token from an android app?
For accessing Google Docs or any other Google service (or any OAuth based service for that matter) you will need to find a way to do an OAuth based authentication, after which you can u get a secure token which you can use to access a service based on the users credentials.
There are some really good examples to get you started:
This is an example of getting AccountManager to work with a Google service like Google Tasks, this shows you how to generate tokens and then how to use them: https://developers.google.com/google-apps/tasks/oauth-and-tasks-on-android
This is an in-depth look into how you can authenticate based on the users Android credentials, has an example of how things work and how the UI should be: http://www.finalconcept.com.au/article/view/android-account-manager-step-by-step-2
For something specific to Google Docs have a look at