To create a backup, either tap the «Secure My Funds» button on the main page, or choose «Backup» from the pop-up menu. You will be shown a list of words, one after the other. Write those words down with pen & paper. You will then be asked to retype the words to confirm that they were written down correctly. Store this word list in a safe place! Anyone who gets access to this list will have access to all current and future funds in your wallet!
Once the backup has been completed, you cannot see your word list again unless you have a PIN set. This is to prevent others from getting to your current or future funds, should they get access to your phone.
Note: The backup procedure only backs up your HD accounts. Your classic single address accounts are not part of this backup procedure. After setting a PIN and a waiting time of 288 blocks (2 days) you can create additional backups of your HD accounts.
If you still need to back up a single address account, you can still get access to its private key by selecting the account and choosing «Export» from the pop-up menu.