Backup is the most important thing you must to do when you use this application. Backup procedure will securely store your accounts and wallet data.
When you are creating new account, you must to save your seed phrase, that can be used for the restoration procedure.
But the best way is to use keystore file, that can export all accounts together with (without) transactions, contact list, etc.
How to create backup in keystore format, you can learn on this page
How to see public/private keys (NOT recommended for backup, but need for developers for some cases), you can learn on this page