Hi plsehelp,
Welcome to the Apple Community.
Your Apple ID and password are the ones to use for everything Apple, including iTunes and the App Store etc.
Wondering if you tried following the steps in the above article.
That will help you update the new Apple ID password to be the same, in everything Apple.
If it is the first time you use the App Store and iTunes,
you need to have a payment method listed in your Apple ID account,
to use the apps and services, even if you are only downloading free items.
First: Check the payment methods that you can use with your Apple ID:
(Scroll down to see the various countries listed)
https://support.apple.com/en-us/HT202631
Now you can:
Change, Add or Remove Apple ID Payment methods
https://support.apple.com/en-us/HT201266
After you have used the App Store / iTunes for the first time,
you can delete the payment method if you wish.
Hope this helps you :)