You don't setup Airport Express in the iPod Touch. I'm assuming you mean setting up a wireless network in the 802.11b/g/n variety (WiFi). You do that on your computer, a PC or Mac. An Airport Express is a wireless router that allows other computers, smartphones, iPhone and iPod Touch to join the wireless network. If the wireless network has an internet connection, you can browse the web using those devices.
You setup your iPod Touch to join a particular WiFi, including the one you may have at home, and other WiFi hotspots such as coffee shops, hotels, airports, shopping malls etc. This is done through the Settings->Wi-Fi screen on your iPod Touch and you just pick and choose a specific network you wish to join. Some public WiFi networks are free and don't require a password, but most others do. Even for those that don't need a password, when you try to browse the web, you may be first presented with a page requesting you to signin or pay ($$$).
Hope this helps.