1. Buy a wireless router.
2. Buy ethernet cables for wired computers, wireless adapters (as needed) for wireless computers.
3. Connect computers to switch w/ cables or wireless, as appropriate.
4. Configure each computer’s TCP/IP network settings w/ DHCP (probably already is by default).
5. Connect ISP’s device (cable modem, dsl modem, etc.) to WAN of wireless router (ignore this step if you don’t need internet access).