One great thing about Google Apps is that everything is compatible with the Google account you (more then likely) already use on a daily basis. Also, Google has released three versions of Google Apps to suit the needs of both casual users and business professionals alike.
Google Apps For Personal Use (at home casual user) - Google Apps for personal use is the most basic of the three Google Apps packs. This version is offered completely free and can be accessed directly through your Google Account. It offers Gmail, Google Talk, Google Calender, Google Docs, and Google Sites all in basic form.
Google Apps Education Edition - Google Apps Education Edition is aimed at teachers, school officials. Schools choosing to transition to Google Apps, will allow for better communication between students and staff, easy install on clasroom computers, compatibility with other schools and universities, and more. Basically, Google Apps Education Edition is a new alternative and standard available for schools to use vs. Microsoft office.
Google Apps For Business - Google Apps For Business is the highest end edition of Google Apps. It features the same main components as Google Apps Personal, plus more storage, more efficient spam control, better security, uptime, and much more. Cost for Google business is reasonable currently at $50 per user a year.