A private key gives you access to a specific wallet, allowing you to manage the funds within and perform various operations, such as exchanges and transactions. They can be used to import wallets that you created on other services into Guarda, or the other way around.
Please be very careful while managing your keys. Store them in a highly secure place. Any person who gets their hands on your private keys will gain access to your funds. Never share your keys with anybody, not even Guarda team members.
On Guarda, all of your keys are already stored together and encrypted in your backup file - but it is still important to save individual private keys for your currencies.