Of all the sharing features built into Mac OS X, File Sharing is the most commonly used and has been around the longest. By turning on File Sharing, you can enable other users to access selected folders on your Mac according to the criteria you specify, and you can access any of your own files when using another computer. File Sharing can use AFP (Apple Filing Protocol), FTP (File Transfer Protocol), SMB (Server Message Block), or any combination of these.
As with all shared resources, File Sharing works as long as other computers can see your Mac over the network. Barring any restrictive firewall or router settings, that should always be true on your local network. If your Mac has a publicly routable IP address (or uses port forwarding), File Sharing can reach it over the Internet, and if you use Back to My Mac, you may be able to contact your Mac remotely, even if it's behind a NAT gateway.
You can turn File Sharing on with just a few clicks, but after you do so, be sure to read the remainder of this section to learn what settings you may want to adjust.
To activate File Sharing, follow these steps:
Choose System Preferences to open System ...