A friend asked me about this a couple of days ago, so I figured I’d write it down.
The NFT standard commonly used on Ethereum is ERC-721, where each NFT is distinguished by a unique tokenId.
NFT prices are determined by buyers’ and sellers’ offers. Trading activity is usually lower than for fungible tokens, so there may not be anyone willing to buy when you want to sell.
Minting and trading NFTs on Ethereum both require paying Gas with $ETH .
Leave a comment if you understand; if not, ask away in the comments.

For reference only; not trading advice.