Does your modem have an Ethernet connection? If so, you're halfway there.

What you need to get is a wireless router - the modem connects to the router via the Ethernet cable, and then you can configure the router to work with your wireless devices - but Wireless [Wi-Fi] is pretty much a plug-n-play technology.

Whilst you can get modems with built in Wi-Fi routers, I think that a router that connects to your modem is better, in case you change the way you connect to the Internet [e.g move house.]