ETFs replicate the holdings of indexes and can follow specific industries, regions, etc. If you are looking to diversify your investments, hedge your risk, or gain exposure to a certain market, then ETFs may be what you're looking for.
For example, many investors love Tesla and believe in the company's competitive advantages. However, it's an incredibly volatile stock and some may want to participate in its upside but limit exposure to volatility. ARK Innovation ETF ("ARKK") is an example of a technology ETF, and Tesla is roughly 11% of its holdings. You can indirectly "buy" Tesla by buying shares of ARKK, which is comprised of many other technology, healthcare and consumer businesses.
All in all, ETFs are a popular investment vehicles as ETF investing essentially provides a diverse group of holdings with a single transaction.