What is the structure of building a wireless network?

The Modem receives the internet data signals from your ISP (Via ADSL line, cable Modem, wireless connection…etc) and convert and transmit those data to the Wireless Router via a Network cable.

Note:
The Modem is transforming the Internet data signals from one medium (such as a ADSL connection medium) to an Ethernet medium (or we can call it LAN which is a network type used normally for home networks which is the abbreviation of Local Area Network) to make the data understandable for the computers and the devices. The Wireless Router receives those data signals and transmits them to all the network terminals via wireless network medium.

Note:
You can setup your wireless network without a Wireless Router in case if your Modem has a Router capabilities like the most of the new internet Modems. The network terminals such as Computers and laptops have Wireless Adapters which communicate to the wireless network and complete the connection with the Wireless Router.