Read this book to learn the answers to questions like:
Which technique should I use to share my files?
How do I set up my Mac as a file server?
What types of security should I set up? Do I need a firewall?
Should I use Samba or AFP as my file-sharing service?
How can I restrict what users can do after they log in?
How can my Windows-using colleagues access my shared files?
How do I share iPhoto photos? What about songs from iTunes?
What's the best way to connect to a file server from my Mac?
What are my security options for running an FTP server?
How can I configure my server so it wakes up if someone wants to use it?