There’s going to be three apps altogether. When you try to edit a document or spreadsheet in the mobile Google Drive app, you’ll be prompted to download the standalone Docs or Sheets apps respectively. It’s already available in the Play Store and iOS App Store. If you refuse to use these new apps, then you’ll only get to view the files.
Later, presentation editing will come via the Slides app. It’s not yet available right now.
I’m certainly not sure why Google felt it necessary to fork out the editing functions into a separate app. This move comes not long after Microsoft’s recent Office for iPad. This may be Google’s attempt to raise the profile of its own office productivity apps.
Office for iPad is really good. However, editing capabilities do require an Office 365 subscription. Google’s apps, on the other hand, are free.