Syncing your Google Drive files and folders in your Android device, can be done either manually or automatically. Start syncing all your documents stored in the Drive, by doing as follows:
1. Open "Settings" app
2. Go to accounts and tap "Google"
3. Tap the Google Account you would like to Sync drive
4. If you have disabled auto sync option, you need to tap Sync Drive to start syncing manually
5. If syncing option is already enabled, you just have to make sure that Sync Drive is marked too. So the device automatically syncs your Google Drive account as well as other Google services