Local or Business?
Local (or less then 10 computers) is quite easy. You can buy a standard router at most best buy / computer plus / Staple stores and just use ethernet to wire them in. The router will autoset most settings to get you started.
A business requires much much more.
Answer these questions for me.
How many computers?
How many Servers?
Printers?
How many locations (does this project spand to multiple sites?)