Non-Fungible Tokens (NFTs) are transforming the digital art by allowing artists to sell unique, one-of-a-kind digital artwork that is verified on the blockchain. Although NFTs have attracted much attention from academia and industry, little is known about this innovative art practice. In this work, we focus on how NFT artists understand their art creation process, interact with NFT marketplaces, and face challenges in their NFT practices. We conducted a mixed-method study, including interviews with 19 artists and an analysis of market transactions on OpenSea and SuperRare. We found that serialization and Web3 concepts are significant features in NFT artwork creations, and artists utilize artificial intelligence and smart contracts to create artworks incorporating these features. Artists perceived that blockchain features like transparency, openness, and authentication strongly influenced their NFT trading experiences, and they also encountered challenges such as determining artwork value, rights ownership, and addressing technical issues in the creation process.