Crypto wallets are a secure way to store your cryptocurrencies. They allow you to store different currencies separately so that you don't have to worry about losing them if one of your cryptocurrencies suffers a hack. With Metamask, you can also use their wallet to handle Ethereum and other altcoins. You can use their online interface to buy and sell cryptocurrencies, or you can use the wallet's app on your phone. Metamask is one of the most secure wallets out there, and it's easy to use.
