Networking 
Sharing files over a network
All Macs are equipped with an Ethernet card. You can use this to connect your Mac to any network, including modems, hubs, switches and routers. You'll need an UTP Ethernet cable. If you only want a small network between two computers, you'll probably need a 'cross over' cable. Are there more computers in the Network and you connect to a hub or switch, you'll need a 'straight' cable. Just go to a computer store and tell them what you want, they'll know what to sell you.
What should I do to connect my Mac to an existing network:
Mac- to- Mac, Mac-to-Windows, Mac-to-Linux/Unix
Connect your Mac with an UTP cable. Go to System Preferences => Network. Make a new configuration and call it 'LAN' (Local Area Network).
Choose 'Build-in Ethernet' at 'Configure Network ports'
When you want to communicate with older Macs (pre OSX) go to 'AppleTalk' and make it active. Otherwise this is not necessary.
Choose 'Apply now'.
Now go to System Preferences => Sharing and edit your Firewall.
You can access the Network in any Finder Window by selecting 'Network':
-
Or you can go to the Menu "Go" and "Connect to server":
and choose 'Browse': 
Now use the password the Network Administrator gave you. Otherwise you can log on as 'Guest':
After logging on, you see the volumes you can access at the server:
After selecting, click 'OK' and the Volume will appear on you Desktop and in any Finder Window:
Note: You can tell your Network Administrator your Mac communicates with the SMB or 'Samba' protocol.
Now let's show how your Mac can be a server: Linux/Unix-to-Mac, Mac-to-Mac
First you'll need to give your Mac permission. At default, your Mac is closed to others. So you'll need to go to System Preferences => Sharing and Choose 'Personal File Sharing':
Sharing files.
Clicking on the 'Home' icon in the Sidebar brings you to your Home Folder immediately. Your Home Folder is private; only you can read its contents. Only the 'Public' folder is accessible by others in a network:
They only are allowed to drop stuff into the 'Drop Box'.
TIP
Public access to any other folder
At default, only the Public folder is accessible to others.
In case you want to change that, select a folder and choose 'Info' from the Archive Menu. Now change the access details at 'Ownership & Permissions:
Windows Sharing: Windows-to-Mac
To let a Windows computer access your Mac you'll need to create a new account (or modify an existing account).
In this case, I choose to make a special account, called 'Windows User'.
1. Go to System Preferences => 'Accounts'
2. Use the '+' symbol to create a new account. Here: 'Windows User':
At the next picture, the account has been created:
3. Go to System Preferences => Sharing and choose the 'Windows Sharing' option. A dialogue box appears. Choose the account you want to open to Windows access:
Now Windows Users can logon to your Mac using the log on name 'windowsuser' and the password you created.
Note: More details about other users in the 'Users' chapter.
TIP
Use your Mac like a router
If you want to share your Internet connection, use the 'Internet' section of the 'Sharing' SP.
After that, go to 'Firewall' and turn on 'Personal Web server. Otherwise your Mac won't let the other computer pass!
A FireWire Network: use a second Mac as a hard disc
You can connect two Macs through a FireWire cable. One of them boots normally, and the other only functions as an external hard disc.
Shut down both computers. Connect the FireWire cable. Boot ups the first computer normally. After boot up, start up the second computer (the one who's going to function like a hard disc) with the T key .
This Mac will not boot normally, but will only function as an external FireWire hard disc. We call this 'Boot up in Target-mode'.
Now you can transfer data from one Mac to another.
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