In SharePoint, documents are typically stored in what's called Document Libraries.  Document libraries are basically a group of documents.  You can do much more with document libraries, but in this topic just know that it is a place to store a group of documents.

Inside a document library you can:

• store your documents so that they are available to your colleagues anywhere and on any device that has access to the Internet. 
• receive an email notification when a document is uploaded or modified.
• organize your documents so that only certain people have access to them.  
• email your document to SharePoint for quick uploads.  
• access your files straight from Outlook.
• automatically sync the documents on your computer to & from SharePoint by using SharePoint Workspace.
• create workflow rules that can move documents to follow your business processes such as time sheet submission.