The Complete Guide to Using the iTunes Store
Can't connect to the iTunes Store
iTunes: Advanced iTunes Store troubleshooting
Best Fixes for ‘Cannot Connect to iTunes Store’ Errors
Try this first - Reset the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons.
This works for some users. Not sure why.
Go to Settings>General>Date and Time> Set Automatically>Off. Set the date ahead by about a year.Then see if you can connect to the store.