This is called day trading, you need to have a lot of experience to profit like this, for those who don't have much knowledge, I suggest simply buying, holding and selling at a high.

How to make money from falls?

Take a currency, for example, $ETH , and see how it fluctuates during the day... you will see, for example, today that it is alternating between R$19,750 and R$20,200, more or less... should I buy it when it is at 20,100? The answer is no!

Wait for it to fall between 19,900 and 19,750. Did you buy 1 unit at that price? It went up from 19,750 to 19,900. Should I hold on and wait for 20,200? The answer is no! Sell it for 19,900 and it will probably fall back to 19,750 to 19,800. Then you can buy it back and sell it... it is better to buy 100% than to buy and wait for it to reach a high value. By buying at a low price and selling, you will end up making more profit than if you had waited for it to reach a higher value. Yesterday I ended up losing more than R$1000 with it because I hit my loss in the morning. What did I do? Did I wait for it to go back to 20800 to recover my value? No... I recovered only by buying and selling during the day's dips...

A simple tip, but it might help you in some way.