Android : How to use Google Drive API to Download a Folder to SD Card (Android)

i am new in android, and i am trying to create a simple app in witch i want to download a single folder from Google Drive to SD Card.

i don't know how to use Google Drive API and how to download a folder from Google Drive to SD Card.

please help me: some tutorial or sample app will be help full, also guide how to setup Google Drive API in my app.