Opening a brokerage account is, mechanically, one of the easiest financial steps you'll ever take — it usually takes about 10 minutes online, requires no minimum deposit at most major brokerages, and costs nothing to open. You'll need your Social Security number, legal name, address, and date of birth for identity verification (a federal requirement called Know Your Customer, not brokerage-specific red tape), and you'll choose an account type: a standard taxable brokerage account, or a tax-advantaged account like an IRA.
Since major brokerages eliminated trading commissions around October 2019 (Charles Schwab moved first, with Fidelity, TD Ameritrade, and E*TRADE matching within days), buying and selling stocks and ETFs at brokerages like Fidelity, Schwab, or Vanguard is typically free. Fractional shares — the ability to buy a specific dollar amount, like $20 worth of a stock, instead of needing enough for a full share — mean you can start investing with almost any amount of money, not just whatever a single share happens to cost.
Correct moves you up, wrong moves you down — reach 100 to master this lesson.