An index fund is a shopping cart, not a stock pick

An index is just a list. You cannot buy the list itself. An index fund is the cart that holds what is on it. Fidelity’s Learning Center describes the fund as a mutual fund or ETF that aims to mimic an index such as the S&P 500, pooling many investors so a manager can own the same securities in roughly the same weights.

The S&P 500 tracks about 500 of the largest public U.S. companies, weighted by market size. If the index rises, it does not mean every name went up. Enough did that the average moved. A share of an S&P 500 index fund is meant to move with that average, which is cheaper and simpler than buying one share of every name on the list.

Because the job is to copy, not to pick, fees tend to stay low. Fidelity cites a 0.015% expense ratio on its 500 Index Fund as of April 29, 2025, against 1% or more on many active funds. Index funds also trade less, which can mean fewer taxable distributions. The tradeoff is baked in: you get the market’s average, including the duds, and you do not get a manager who can sell before a drop.

You also do not get to yank names you dislike. If that still sounds useful, the first step in the explainer is an account, then cash, then a fund whose index, history, and expense ratio you actually checked. This is education, not a recommendation.