How to link account

Just set up new ipad and need an app. Select app, press install, sign in with apple id that comes up and enter password, tick say all done then get the message...This apple id has not yet been used in the itunes store. Tap review to sign in then review your account information.. Cancel or Reveiw - when i hit review a sign in requried pops up. Please enter your apple id and password to create an itunes store account from your existing apple id. The place to enter is for a password only and it does't say it's for my id. When i put my password in and hit sign, it repeats the ...this apple id has not yeat been used in thet itunes store etc.

I can't seem to get passed this so therefor can't get the app, is there a way around this or it is an problem?

Any advise is greatly appracited as this is for work.