You used to be able to access your whole Google Drive from one app, but had to sort through your documents, spreadsheets and slides on that app. Now you can download separate apps for your documents and spreadsheets (slides coming soon).
Google Docs and Google Sheets can be found in both the App Store (Docs, Sheets) and in Google Play (Docs, Sheets).
Is this your first time getting the Google apps on your device? Here is a short summary of what each app can do. https://support.google.com/drive/answer/49008?hl=en