19 Feb 2020 That means you can put already taxed income into bonds, index funds, or whatever else, allowing it to accrue compounded interest over time. If 27 Feb 2020 First, let's quickly discuss what an Index Fund (ETF) and a Mutual Fund are. Who better to ask then Vanguard themselves? An ETF is a collection ( 9 Sep 2019 You can invest in an index fund through your 401(k), IRA, or a brokerage account . Your office retirement plan is often the best place to start investing. Roth IRA through a brokerage firm, bank, or other financial institution.