An ETF is a basket full of stocks from many companies at once, in a single purchase, e.g. the S&P 500 (500 US companies) or the MSCI World (1'000+ companies worldwide).
The 500 largest US companies in one purchase, from Apple to Coca-Cola. Historically almost always positive over long periods, despite crashes along the way. The chart alongside shows the real, current price history, a single purchase covers hundreds of companies at once.
Investing regularly for the long term historically beats trying to hit the perfect entry or exit point. Short-term trading tends to be more of a losing than a winning game for most people.
Anyone who invested CHF 200 a month into the S&P 500 since January 1993, despite the dot-com crash, the financial crisis and Covid, would be looking at this by the end of 2025:
That's 8.2 times the amount paid in. Annualised, roughly 10.7 % return per year (incl. reinvested dividends, before tax/fees, excluding the CHF/USD exchange rate, purely illustrative, not investment advice).
Illustrative calculation based on actual S&P 500 annual returns incl. dividends (source: Slickcharts). Past returns are no guarantee of future performance.