Essentially, you can choose to put any of your apps into customizable groups -- just as if they're a separate folder -- and each group you create gets its own tab up on top.
Then, the recipient receives an email with a link, and just has to click, log in (or create an account, ) and will immediately have access to the document or folder.
Now the files that you place in your Google Drive folder on your PC or Mac are stored alongside any files you create in what used to be called Google Docs.
And while most applications have default folders where the files they create (such as the Excel spreadsheet mentioned above) are saved, the path to such a folder may have been changed (by you or another user, either accidentally or on purpose).