The plain version
An exchange-traded fund, usually called an ETF, is a basket of investments you can buy as one share during the market day. An index fund is a fund that follows a list, such as a list of large U.S. companies or a wide mix of companies around the world. Many index funds are ETFs. Some are the older kind of fund that sets its price once after the market closes.
One share can stand for hundreds of companies, or for a pile of loans (bonds). That is why beginners use them. You get a wide mix without researching each name.
A fund that follows a list, and a fund that picks
A fund that follows a list tries to match that list, not beat it. If the list is a broad stock market, the fund rises and falls with that market. You are not betting that a manager found a hidden winner. You are taking the market’s result, minus a small yearly fee.
A fund that picks tries to choose better investments than the list. Some do, for a while. As a group they cost more, and after fees many do not stay ahead. For a first portfolio, the fund that follows a wide list is the simpler default. You can learn the picking version later if you still want it.
How you buy one
You need an account at a broker, the firm that holds investments for you. You search the fund’s name or its short symbol, enter how many dollars or shares, and place the order while the market is open. The price moves during the day, like a stock. You do not mail a form to the fund company for a typical ETF. The broker is the shop window. The fund is what you own.
What to check
Read what the fund owns. “U.S. stocks” can mean the whole market, or a short list of the biggest names, or a single industry. The label on the tin is not enough. A fund of only chip companies is a bet on chips, even though it is still an ETF.
Check the yearly fee, called the expense ratio. It is a percentage taken from the fund, so you never get a separate bill. Broad funds that follow a list are often very cheap. A high fee needs a reason you can say out loud.
See how wide it is. Hundreds of companies in more than one country is a different product from twenty companies in one theme. Wider is the usual beginner tool. Narrow can be a satellite later, not the whole plan.
What an ETF is not
The wrapper does not make the contents safe. A fund full of stocks can still fall hard in a bad year. A fund full of bonds can fall when interest rates rise. “ETF” describes the package, not the risk.
Some funds are built to move two or three times as much as a market, or to rise when that market falls. Those are trading tools. They can lose money fast even when you understood the slogan on the name. They are a poor home for money you need in retirement.
A simple shape
Many people who invest on their own use one broad stock fund and, if they want a steadier slice, one broad bond fund. Others use a single fund that already blends the two. That is an illustration of the shape. The useful test is whether you can name what the fund owns, what it costs each year, and how long you can leave the money there.