I have three desktop computer. One is connect with internet. Also I have 10/100 Ethernet switch. I want to network my 3pc by switch. Tell me how to do this step by step clearly.

It is not clear if you are going to use the pcs in internet sharing.
BTW, interconnecting these pc's requires you to define each PC an IP address. Open Network Connections then right click Local Area Connection. In General tab, click TCP/IP > properties > enter IP Address and subnet mask (ex: 192.168.1.200/ 255.255.255.0)

If you don't have a device with a dhcp server (like a router or modem router) you won't get online through that switch on all computers . The switch is only a passthrough device it won't distribute an ip address to all computers. Try buying a wired router (I recommend a linskys befsr41) and it will help get your desktops online simultaneously. =)