BTC and ETH:
Two main forces
Now let's talk about Ethereum (ETH). If Bitcoin is gold, then Ethereum is like a "digital computer". On its basis, you can create a ton of things: from various applications (they are called dApps, or decentralized applications) to games and even digital art (remember NFTs? They are also mostly on Ethereum!). Ethereum is constantly evolving to become even faster and cheaper. Many new projects are built specifically on it.
So when we talk about the BTC/ETH pair, it's like you're choosing between a reliable way to store money (BTC) and a powerful platform for innovation and creation (ETH).