Though Apple has given a nice auto discover and connect feature for connecting to Wi-Fi networks, there are times when your Wi-Fi router is on and your iPod Touch still giving cannot access to App Store or cannot access to iTunes error. Not much you can do except the basic troubleshooting steps that i will provide you below:
- First check Wi-Fi Internet access is available and router is transmitting, check with other computers in the network if they are able to access the Internet, because sometimes there might be a problem with the ISP, check this before cursing your iPod.
- In normal scenario your iPod will auto connect to the available wireless access point automatically if its a public network and you will be able to access the Internet readily. Select the Access point from Settings>Wi-Fi
- If its a protected network then you will have to enter a WEP/WPA key which is password which authenticates you to access the Access point and Internet through the protected network.
Other Wi-Fi Internet connectivity problem:
You were surfing the App Store a few minutes ago and now it shows error in connecting to the App Store, this errors occurs when your iPod or iPhone temporarily and quietly enter into Wi-Fi sleep mode to save power and battery. To start Wi-Fi again you can turn OFF and ON again or try accessing safari web-browser/Maps apps( this one works good for me) after pages and maps starts loading again try App Store again.
These troubleshooting steps also holds true for other Wireless Devices.