Back Ups! an Important Part of Being Your Own Bank! Most Important Back Up You can Have is the Wallet Mnemonic seed Words Which GUI Wallet Shows on StartUp and You have to Confirm Them by Copy and Paste. You Should Keep them on a Safe Place.
But they are not the only way you can Make a Back Up, You can Also Backup Your .wallet File from Menu >> File >> Backup Wallet, You need to choose a safe Place to Save your copy of .wallet file. You should also remember your Password.
You can Also Export and store Your Private Keys as a Backup.