Working offline with Google Drive, Docs, Sheets and Slides.
For Drive:
Go to drive.google.com
Click on the gear icon 
in the upper right corner then on Settings. On the Settings menu, check the box for Offline then click Done.
For Docs, Sheets and Slides:
Step 1. Open your Chrome browser (must be Chrome. IE, Safari or Firefox will not work)
Step 2. Install the Google Docs Offline app in the Chrome Web Store
Step 3. Go to one of the Google apps and click on the Main Menu. This will activate for all 3 apps.
Step 4. Click on Settings in the Main Menu.
Step 5. Click on the toggle switch next to "Offline".
Read the Google Help info here, Google Offline.
