Bitcoin and Ethereum are the two largest cryptocurrencies, but they were built with different primary goals. Bitcoin was designed mainly to function as a form of digital money, with a fixed maximum supply of 21 million coins, often compared to digital gold because of its scarcity and simplicity.
Ethereum was designed as a broader platform that lets developers build applications directly on top of its blockchain, using smart contracts. This is what makes things like DeFi lending platforms, NFT marketplaces, and many other crypto applications possible, since they are commonly built on Ethereum or networks compatible with it.
For a beginner deciding where to start, it helps to think of Bitcoin as the more singular, store-of-value asset, and Ethereum as the asset tied to a much wider ecosystem of applications. Many investors choose to hold both rather than picking just one.