Something more knowledgeable may be able to correct me here

But it basically allows for a community kept ledger. So take bitcoin for example. If I want to give you a bitcoin then usually all the bank would need to do it update my account and update your account, that's computationally really simple.

With bitcoin, there is no "bank". Whenever a transaction takes place millions of computers compete solving problems for the chance to perform that transaction and update the ledger basically. They're rewarded for doing this work. However it means we have millions of computers doing shit for 1 simple transaction which is bad for the environment. NFTs use this same technology.