Why I can't purchase anything and they alway said can not connect to iTunes store

Try logging out of your account on the iPad by tapping on your id in Settings > iTunes & App Stores and then log back in and see if it then works.

If it doesn't then you could try disconnecting and reconnecting to your network, and/or a soft-reset of the iPad : press and hold both the sleep and home buttons for about 10 to 15 seconds (ignore the red slider), after which the Apple logo should appear - you won't lose any content, it's the iPad equivalent of a reboot.

You could also try closing the iTunes and App store apps via the iPad's taskbar and see if that makes any difference when you re-open them : from the home screen (i.e. not with iTunes or the App Store apps 'open' on-screen) double-click the home button to bring up the taskbar, then press and hold any of the apps on the taskbar for a couple of seconds or so until they start shaking, then press the '-' in the top left of the iTunes and App Store apps to close them, and touch any part of the screen above the taskbar so as to stop the shaking and close the taskbar.

If you are getting a message to contact iTunes Support then you can do so via this link and ask them for help (we won't know why you are getting the message) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

They normally reply, I think, within 24 hours. But if the reply says 48 hours then you might have to wait that long - I'm just a fellow user, I don't know why it might take 48 hours, but they might be busy or short-staffed.