A Google Doc or Document is one of many Google Apps. You can access these apps in your Google Drive. You will want to be logging into your Google email account. At the top of the screen you will see many of the various apps offered by Google. The one you will be working in to create a document is Drive. This is where all your Documents, Presentations, Spreadsheets, Forms, and Drawing will be saved. Any time you need to access one just go to your Google Drive.
The following video explains how to create a Google Doc (word processing file), the basic tools, sharing and saving.