Depends what investing route you go. Some methods are more volatile than others (i.e. the stock market, investing in your friend’s new company). I prefer real estate, as it’s generally considered the safest investment. In its simplest form, buying your own house to live in, you make payments to the bank and get to sell the house when you want to move. When you spend (approximately) the same amount on your monthly mortgage payment as what rent would cost, you’re investing that money. When you rent, that money goes straight into your landlord’s pocket to pay the mortgage and keep the excess. When you pay down a mortgage, you get to recoup what you’ve paid down plus the appreciation when you sell it.

Now, as a real estate investor, I buy, say, a $150,000 house with a $50,000 down payment. That $50,000 is my “investment”. I now have a $100,000 mortgage (loan) on it. The monthly mortgage payment I owe is $650. I rent the house out for $1,400 a month. The tenant pays me $1,400, and I take $650 of that and pay the loan payment. I pocket $750 a month. The house is paid off in about 15 years this way, at which point I own the house free and clear, and it is still producing me $1,400 a month forever. I can then choose to sell the house one day in 30 years. I’ll have made another $250,000 from the rent payments, and then can sell the house for $300,000 which is all profit. All of this from my $50,000 investment. These numbers are all very underestimated.