Because Google Docs, Sheets, and Slides save to a secure, online storage facility, you can create documents, spreadsheets, presentations, and drawings without the need to save to your local hard drive. You can also access your documents from any computer by signing into your Google Account. In the event of a local hard drive crash, you won't lose your saved content.
Since Google Docs, Sheets, and Slides continuously save your work, there's no Save button. The last updated time shows near the menu bar.