Multiple Nifty's wallets are created if you, at some point, signed up using an email address and then logged in using Twitter.
It's beneficial to know which address is which to determine where your claimed NFTs are located, what your DAI balance is and which wallet it's associated with, and what NFT is located on each wallet for the ability to sell.
You can view your addresses (and determine which wallet is which) by clicking on your profile and clicking the Wallet button located on the left on your profile sidebar:
From there, you can see your associated account wallet addresses and which address is which:
What if I can't determine which NFT is associated with my address?
At this time, there is no available feature on Nifty's to show which wallet houses each NFT. However, should you have any questions, please connect with us via a support request and we'll be happy to help and provide any details you may need!