You'll find the answers to these questions and more:
Why do I have I log in to my Macintosh?
Why do my files reside in the Users folder?
What is the purpose of an Administrator account?
How can I take advantage of the Guest account?
How do I limit time of day when my child can use the Mac?
Can I control who my child exchanges email with?
What's the best way for users on my Mac to share files?
How can I customize the way my login window behaves?
How can I speed up the log in and log out process for everyone?
Can users on my Mac share my iTunes songs or iPhoto images?
What's the difference between a login item and a startup item?