Exchange-traded funds are like stocks. Except they're not. More shares can be created (or redeemed) as the day goes on.
Exchange-traded funds are like mutual funds. Except they're not.
ETF shares get priced all day long, mutual fund shares only at the end.
Exchange-traded funds threaten market stability. Only they don't.
Here's a glossary of ETF terms to get you familiar with how they work.