The stock market remains volatile but not quite as frantic as earlier this year. Meanwhile, the major market indexes remain well below their recent highs.

Against this backdrop, now is a great time to invest in high-quality exchange-traded funds (ETFs) that track indexes. ETFs are a collection of assets that trade as a single unit and are a great place for new and experienced investors alike because they bring instant diversification with the flexibility to be traded like a single stock.

And $500 is a great starting point -- but just that. The key to investing, particularly with ETFs, is to contribute consistently over time. It's a strategy known as dollar-cost averaging, where you regularly invest a set amount at a specific time. This could be with each paycheck or on a particular day of the month.

It is important to stick with this strategy, whether the market is up or down. Down markets are a great time to pick up stocks on the cheap and get a better cost basis.

And you should continue to do so even in bull markets, which tend to last a long time. In fact, according to a JPMorgan Chase study, since 1950, the S&P 500 hit a new all-time high on 7% of its trading days, and on a third of those days, the index never dropped lower.

Let's look at three great index ETFs you can begin to invest in right now.

The Vanguard S&P 500 ETF

One of the most popular ETFs in the world is the Vanguard S&P 500 ETF (VOO -0.14%), and for good reason. As the name says, it tracks the roughly 500 largest companies that trade on a U.S. stock exchange. The index is market-cap weighted, which means that the larger a company's value, the bigger part of the portfolio it occupies.

And as with most Vanguard ETFs, it comes with a minuscule expense ratio. Even seemingly low expense ratios, such as 1%, eat into returns over time, especially as your investments grow in size. The Vanguard ETF's expense ratio is only a scant 0.03%.

With this Vanguard ETF, investors get an instant portfolio of the companies that have grown to become some of the world's largest. The index is also generally considered the benchmark for the U.S. stock market as a whole.

The ETF has a long history of solid returns. Over the past decade, it has generated an average annual return of 12.3%, as of the end of April.

The Vanguard Growth ETF

Sticking with Vanguard and its low costs, the Vanguard Growth ETF (VUG -0.09%) is another great option. It mimics the CRSP US Large Cap Growth Index, which is essentially the growth side of the S&P 500. It has a similarly low expense ratio of 0.04%.

The Vanguard Growth ETF gives you an instant portfolio of many of the large-cap growth stocks that have been helping drive the market over the past several years. It is heavily weighted toward the tech sector, which makes up about 57% of its holdings. And some very tech-heavy companies, such as Amazon and Tesla, are categorized into other sectors.

If you're looking for exposure to the so-called "Magnificent Seven" stocks (Apple, Alphabet, Amazon, Meta Platforms, Microsoft, Nvidia, and Tesla), this ETF is a good option. At the end of last quarter, these seven stocks accounted for over 50% of its holdings.

This fund has been a strong long-term performer, generating a 14.5% return over the past 10 years, as of the end of April.

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The Invesco QQQ ETF

Beating the returns of the S&P 500 is not an easy task, but one ETF that has been able to consistently outperform it is the Invesco QQQ ETF (QQQ -0.04%), which tracks the performance of the Nasdaq 100. Like the other indexes mentioned above, the Nasdaq 100 is also market-cap weighted. It contains the 100 largest nonfinancial stocks on the exchange.

That index has historically attracted fast-growing companies, particularly in the technology sector. As such, it is also very heavily weighted toward tech, checking in at a similar 57% to the Vanguard Growth fund.

The Invesco ETF has been the best performer of these three over the past decade, with an average annual return of nearly 17% over the past 10 years, as of the end of April. And this has not been just from a couple of big years of outperformance. On a rolling 12-month basis, it has outperformed the S&P 500 more than 87% of the time over the past decade (for the period ended March).

It carries a 0.2% expense ratio, but its consistent outperformance over the years more than justifies its higher cost.