High-yield savings accounts pay significantly more interest than traditional savings accounts. They are a safe place to park money you might need soon, like an emergency fund or short-term savings.
The main benefit is liquidity. Your money is accessible, and in many cases the account is FDIC insured. The trade-off is that returns are lower than what you might expect from long-term investments.
For goals within the next few years, a high-yield savings account is usually a better choice than the stock market.