With the release of iOS 7.0.3, Apple also activated a new feature called iCloud Keychain. This allows you to store passwords and credit cards and then have them automatically entered when using other Apple devices too. 
Enable iCloud keychain
To get started, you need to turn iCloud Keychain on. Open the Settings app, select iCloud, tap the Keychain option and turn it on. You’ll then need to enter a four-digit passcode, or use the one that you have for unlocking the screen. Make sure you remember this code as you’ll need it to view your passwords or to reset. 
You’ll then be asked to enter a contact phone number so that it’s possible to receive SMS messages from Apple that’ll be used to confirm connections on other devices.
AutoFill
To start saving your passwords, return to the main Settings menu and select Safari. From here tap the Passwords & AutoFill option and turn on the Names and Passwords option. Now when entering a website through Safari, you will be asked if you would like to save the details. If you do, this will be added to your iCloud Keychain and accessed by tapping on the Saved Password option.
You can tap on any of the entries and enter the passcode you set up earlier to see the full details, including the password.
Credit Card Details
As well as saving passwords, you can store credit card details in iCloud Keychain. From the Safari settings screen, turn on the Credit Cards option at the bottom of the page.Now tap the Saved Credit cards option below this followed by Add Credit Card and enter the required details.
Now, when entering payment details into a web page in the Safari app, you’ll see the AutoFill Credit Card option just above the keyboard. Tap this to enter your details.
Enable elsewhere
If you have other Apple devices then you can activate iCloud Keychain on each one to sync passwords and credit card details between them. On another iOS device, such as an iPad, follow the same instructions to set it up as you did for the iPhone. If you have a Mac running OS X Mavericks, you can enable it by opening System Preferences, selecting iCloud and turning on the Keychain option.
Your iPhone will then receive a notification and ask you to confirm that you have enabled iCloud Keychain by entering your Apple ID password. Once you do, saved passwords and credit card details will be copied across.
More Features
A nice side effect of iCloud Keychain is that it will also copy passwords over for protected Wi-Fi networks. If you connect on your iPhone and then want to connect via an iPad, the password will automatically fill when trying to connect to the relevant Wi-Fi. Keychain can also be built into apps, so look out for developers trying to include this feature in coming updates or new apps. Keychain is a great way to save passwords and credit cards and well worth setting up, even if you only possess one Apple device.