If your capital is 100 pounds and the price of a gold ingot today is 100 pounds and you want to invest in gold, then naturally you go and pay the 100 pounds to get the gold ingot and go.
If the price of gold rises by 10%, then you will have 110 pounds, and if it decreases by the same percentage, you will have 90 pounds.

But because humans are greedy by nature, the stock markets can exploit human greed and say instead of buying one ingot with your money, how about you put this money with me as collateral, and I will buy you 10 ingots in your name.