As Debian is a fully free Operating System. This means that if your hardware has any non free firmware, the drivers may not be available during the install. There are several ways round this.

1. Use the non-free ISO
2. Create a media that has the drivers available so that the installer can scan and install the appropriate firmware drivers during install. The instructions for this are available here.

Another option is to use hardware that does not contain proprietary firmware. Some links below may be helpful.

• USB Wifi Dongle USB 2.0 Wireless 802.11n USB Wifi Adapter
• FSF Certified Wifi hardware (article)
• List of computer hardware that works with free software
  • WiFi cards
  • Ethernet cards