How do NFTs work?

NFTs are different from ERC-20 tokens, such as DAI or LINK, in that each individual token is completely unique and is not divisible. NFTs give the ability to assign or claim ownership of any unique piece of digital data, trackable by using Ethereum's blockchain as a public ledger. An NFT is minted from digital objects as a representation of digital or non-digital assets.

Scarcity

The creator of an NFT gets to decide the scarcity of their asset.
For example, consider a ticket to a sporting event. Just as an organizer of an event can choose how many tickets to sell, the creator of an NFT can decide how many replicas exist. Sometimes these are exact replicas, such as 5000 General Admission tickets. Sometimes several are minted that are very similar, but each slightly different, such as a ticket with an assigned seat. In another case, the creator may want to create an NFT where only one is minted as a special rare collectible.
In these cases, each NFT would still have a unique identifier (like a bar code on a traditional "ticket"), with only one owner. The intended scarcity of the NFT matters, and is up to the creator. A creator may intend to make each NFT completely unique to create scarcity, or have reasons to produce several thousand replicas. Remember, this information is all public.