ETFs trade on stock exchanges just like stocks. You can buy and sell ETFs through your brokerage account during regular market hours (when the stock exchanges are open). Many brokers today offer commission-free trading for ETFs; however, ETFs charge fees, known as expense ratios. The expense ratio is listed as an annual percentage. For example, a 1% expense ratio means you'll pay $10 for every $1,000 you invest in the ETF. The expense ratio can take a significant bite out of your profits, so it's important to compare expenses when researching ETFs (and mutual funds).