Answer to the question How To Share Internet Connection Over Wifi should be addressed in at least 2 different ways. That itself points out that more than 2 ways on How To Share Internet Connection Over Wifi is possible. Lets do look at how things can be done the easy way.
Ad Hoc Way
For this the basic requirement would be at least one computer running in Microsoft Windows based Operating System. The feature you are to use s the ICS a.k.a Internet Connection Sharing. The ICS opens the possibility of connecting more than multiple computer the same time to the Internet with the use of a single computer connected to the Internet. You can do this to share connection with Windows based Operating Systems and other non Windows based ones.
First you can log in as administrator to the computer running on Windows Operating System. Launch your Control Panel and then open up the Network and Internet panel. From here you can click on the View Network Status And Tasks and by the Network and Sharing group, you can find the option Set Up A New Connection Or Network. Click it and select the Set Up Wireless Ad Hoc (computer to computer) Network option. Follow the wizard to complete the configuration and with that you can enable a temporary network to share files between computers or an Internet connection. You would need to provide a name for the network you want to create, the chose the security type of the connection. You need to note that an open connection would never need a password, while WEP or WPA2 will only allow users who enter a password to use the shared connection. Finally you need to select the option Turn On Internet Connection Sharing before you can let other computers use your Internet connection.
If you got a broadband modem for Internet connectivity, the easier way to make the connection go live with out wires and to share the Internet connection over WiFi would be a wireless router. You can bring in a wireless router between your broadband modem and the computers or other WiFi enabled devices. The network created here is a permanent one unlike the above mentioned ad-hoc. So be sure to get a router (preferably n router) with adequate range and you can refer my article Top 10 Wireless Routers, to get to know a basics before you get a wireless router. So, get one router, plug in the cable from your broadband modem to your router, plug in the router adaptor, configure and start sharing Internet connection over WiFi.