There a generally several steps you need to take regardless of the trading platform you use:
Find a reputable broker online and set up a brokerage account on their website.
Fund your account through an available payment method.
Navigate to the NFLX stock, enter the number of shares (or how much you want to invest with fractional shares), and select your preferred order type (market, limit, etc.).
Execute the trade.
Evaluate your position regularly.