You'll need to set up offline access while you still have internet access in the Google Drive app to be able to view a file offline and in Docs, Sheets, or Slides app to be able to edit it. Here's how: Set up Offline Access I. And, if you make a file available when offline, you can access it even when your device isn't connected to WiFi or a network connection. The Google Drive App (for iPhone/iPad and Android) allows you to access (view, share, star, rename files also edit Google Documents) Google Drive files from your mobile device. Follow the directions below for setting up Mobile Devices and your Computer so you're prepared. Once you regain internet access, any offline edits will be synced. Keep in mind that if you make edits while offline, collaborators will not see your edits and any edits collaborators who are online make will supersede your changes.
You can use many Google Apps features offline, but only if you first set them up while you have internet access.