If you already have a Roku account, there's no need to create a new one. If you're not sure of the email address used on your Westinghouse TV you can find it under Settings->System->About.
It's been a while since I've set up a device from scratch, so I don't remember exactly how it goes (and it's probably changed since the last time I did it), but this is the best information I could find:
How to activate or link your Roku® streaming device | Official Roku Support
It's possible that it may still ask you to attach a credit card to your account at some point, but it's not necessary. Once your TV is linked and starts downloading your channels/apps you're really finished with the linking process and can skip the rest unless you want to take advantage of some of the offers for new devices (which will require setting up a credit card).
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