Whenever you are storing objects with a market value, security is necessary. This applies to barter systems as well as economies using currency as a medium of exchange. While banks store balances on a private ledger, cryptocurrencies store balances under unique addresses on a distributed public ledger. The cryptographic private keys to access the balance stored on each public address are therefore the object of value in this system. This section of the documentation discusses different practical methods of keeping these keys safe in wallets, while still remaining useful for day-to-day needs.
For safety, it is not recommended to store significant funds on exchanges or software wallets. If you are holding cryptocurrency worth more than the device you use to store it, you should purchase a hardware wallet.