Here are some resources on how to use Gmail and Google Apps:
Official Google Resources
Gmail Getting Started Guide [2]
Gmail Help [3]
Other Resources
GMail User Tutorials [4]
Links:
[1] http://metavisual.com/using-gmail-and-google-apps
[2] http://mail.google.com/support/bin/answer.py?answer=90877&topic=12925
[3] http://mail.google.com/support/?ctx=about&hl=en
[4] http://www.gmailusers.com/tutorials.htm