Google Docs enables multiple people in different locations to collaborate simultaneously on the same doc from any computer with Internet access. For example, Alice and Meredith are working on a project together, and they need to write a document, keep track of their work in a spreadsheet, and create a presentation to share with other people involved in the project. Alice lives in New York, and Meredith, in Los Angeles.
When Alice makes changes to the document, spreadsheet, or presentation, Meredith can see them in real time and respond to them immediately. Both of them work on the same docs, so there's no need to go back and forth, comparing and consolidating individual files.
To start collaborating in Google Docs, simply sign in with your Google Account. If you don't have an account, create one now.