How to keep your currencies from being lost?

I have a friend of Arab nationality who has been interested in e-commerce since 2005 before the issuance of cryptocurrencies. One day, after the afternoon prayer, he told me that in early 2009 or 2010, he received an email from someone named Satoshi explaining a white paper about a currency called Bitcoin, and at the end of the paper, there was his personal email for contact. My friend said he was surprised by this electronic currency; I didn't understand the terms, they were new to me. He said he contacted Satoshi via email and asked him a specific question: What is Bitcoin, and can I earn from it, and how do I buy it, and what is its price? He said he answered me with answers I didn't understand: blockchain, mining, and decentralization, and a lot more. I said, 'Dear Satoshi, I don't understand what you're saying. Will this currency be exchanged in the markets?' He told me, 'Yes, I assure you that.' I said, 'Okay, what's its price? I have $80; if I convert it to you, how much will you send me?' He said, 'I will send you 8,000 coins,' and we agreed, and he sent me the coins with twenty-four words. He told me to keep them safe. I asked him, 'Do you expect the price of the coin to reach a quarter of a dollar, or half, or a dollar so I can sell it?' He said, 'Yes, of course.' The important thing is that I watched its price for a month; the price went down and did not rise. I said, 'Unfortunately, this scammer Satoshi has deceived me,' and my friends in a famous Arab forum said, 'Yes, he is the biggest scammer; beware of him; there is no such thing as a digital currency.' I tore up the paper, and to this day, I regret that I lost a fortune.