When it says incorrect password, this doesn't mean you have to create a new password every time.
To access iTunes, App Store, iBooks Store and iTunes, you have to be logged in with the same Apple ID on iPad and iTunes on your computer, or else they won't work together.
Try this:
Go to this website:
https://appleid.apple.com
Select "Reset your password" and follow the instructions. Choose a password and write it down. It's important to remember capital letters and all the various signs you enter, like.,?!#...
Answer your security questions, or verify using email or get a recovery key, if you use 2 step verification.
Change the password and use it on your iPad and in iTunes afterwards.