You probably need a wireless router designed to work with your modem -- assuming Roadrunner (is this a cable company ?) supplies a modem.
Best visit a decent retailer and explain the situation or call ISP (Roadrunner ?) and ask what they usually recommend. The router manual will have instruction on connecting -- and most brands have a software wizard which will lead you thru it.
Bear in mind that the computer(s) will also need a wireless adapter -- and wireless is less reliable and slower than a wired connection.