Weeks go into choosing what to buy, and some new investors never buy anything. The choice is smaller than it looks. For a beginner, the decision that matters is a plain one: own a wide slice of the market, and pay as little as possible to do it.
Your first day
Open an investing account and buy one broad index fund with money you won't need for at least five years.
Choose the long-term account your country offers, such as a TFSA in Canada, a Roth IRA in the US (a retirement account, so withdrawing earnings early can be taxed and penalised) or a Stocks and Shares ISA in the UK, at a low-fee broker that charges no monthly account fee. Opening takes about ten minutes of forms with ID and a bank account, and the first transfer can take a few business days to clear.
When the money arrives, search for a fund that tracks a total market or the S&P 500, or a global index if you'd rather spread across countries. Check its expense ratio, the yearly fee, and pick one around 0.2 percent or less. US and UK broad funds are often near 0.05 percent, and Canadian ones are usually somewhat higher. Buy it with the whole amount.
You're done when the fund shows in your account with a number of shares next to it. You now own a small piece of hundreds or thousands of companies at once. The balance will move every day, and drops of 10 percent or more happen in about half of all years. Check it weekly at most, and don't sell because of one bad week.
The thing most people miss
One fund, chosen mostly for its fee, sounds too simple. The fee is the point. A fund charging 1 percent a year against one charging 0.05 percent looks like a rounding error, but on 10,000 dollars growing at an assumed 6 percent a year before fees for thirty years, it ends near 43,000 dollars against 56,600. Nothing else changed except the fee.
Picking winners doesn't close that gap. Over periods of ten years or more, most actively managed funds have trailed a matching index, because beating the market is hard even for professionals and their higher fees start them behind. A beginner doesn't need to outguess the market. Owning all of it cheaply and leaving it alone already beats what most funds deliver after fees.
What not to do
Don't invest money you might need within five years, including your emergency fund, because a market drop right before you need it turns a temporary loss into a real one. Pay off high-interest debt such as credit cards first, and if your employer matches retirement contributions, take the match before anything else. This is general information, not advice for your situation, and an index fund can lose value.
The next step is to automate it: a fixed amount moving into the same fund on the same day each month, whatever the price. It removes the decision you would otherwise make every time the news looks frightening, and that decision is where beginners tend to go wrong.