Hi Rahajeng,
I assume that it is the first time you're using iPhone? If so, I'd like to highlight the importance of having an Apple ID for every Apple devices.
Allow me to quote from Apple Support:
"An Apple ID is your user name for everything you do with Apple, such as shop the iTunes Store, enable iCloud on all your devices, buy from the Apple Online Store, make a reservation at an Apple Retail Store, and use certain resources on the Apple Support website (apple.com/support)."
As you can see, the Apple ID is like the main essence for enjoying any Apple devices that you've purchased. You can actually create this Apple ID the exact time when you buy your iPhone 6 at Apple retail store. Just ask the store clerk if you'd like the ease of creating Apple ID.
If you'd like to create custom Apple ID, simply follow these steps:
1. Open the App Store
2. Select any application that you'd like to download (I prefer any apps that are FREE, of course)
3. While trying to install the application, there will be dialog box that suddenly pops up
4. Select the 'Create a New Apple ID' button
5. You will then be redirected to registration form
6. Afterwards, simply fill in your personal information as detailed as possible
7. If successful, there will be a validation request sent to the specified email address
8. Click the validation link, so that your Apple ID can be validated
That's it! You've successfully created Apple ID and able to download any available applications from App Store!
Regards,
Risdian