Cryptocurrencies can be kept online or offline. If the cryptos are kept on the exchange platforms or other online platforms, it can be lost due to hacks.
So it is important to choose the best wallets that are safe and secure. Please help me in choosing the safest cryptocurrency wallets
I recommend using a hardware wallet, if it is for long term storage. But if it's only for the short term, online wallets are great too and I recommend Trustwallet.