All investing involves what is called ‘risk’, which is the chance you can lose money. Some investments are safer (less risky) than others. Generally speaking, the higher the risk, the more money you can potentially earn, but there is a greater chance of making a loss.
But risk is a good thing - it’s what lets you earn money on your investments and build up compound interest over a long time. Sensible investing is all about managing this risk so that you are making a good ‘return’ on your investment, but limiting the chance of losing money overall.