Google Apps is a service from Google providing independently customizable versions of several Google products under a custom domain name. It features several Web applications with similar functionality to traditional office suites, including: Gmail, Google Groups, Google Calendar, Talk, Docs and Sites.
The Standard Edition is free and offers the same amount of storage as regular Gmail accounts. The Premier Edition, which offers additional e-mail storage, is available for an annual fee. The Education Edition, which is free, combines features from the Standard and Premier editions.
Here in these Google Apps Training videos you can gain the undertsanding you need to make use of these services in your business etc.