How to create an Apple ID and download apps on App Store

You don't say what make it incomplete.

This document explains how to add a payment method to your Apple ID on a Mac, Apple mobile devices, PC, or online ➔ Add a payment method to your Apple ID - Apple Support

On an iPhone or iPad (note that the details may vary slightly depending upon which iOS version you are running) :

1. Open the Settings app.

2. Tap your name.

3. Tap Media & Purchases (or Payment & Shipping). You might be asked to sign in with your Apple ID.

4. Tap Manage Payments. Depending upon the iOS version you use you might not see this step.

5. Tap Add Payment Method. Enter the new payment method, then tap Done.

Read this document to learn how to download apps and games on your iPhone or iPad

Download apps and games on your iPhone or iPad - Apple Support

How to get apps for iPhone or iPad

1. On your iPhone or iPad, open the App Store app.

2. Browse through the Today, Games, Apps, or Arcade tabs to find apps you like. Or tap the Search tab to look for something specific. If you find a game that says Arcade, subscribe to Apple Arcade [at: Join Apple Arcade - Apple Support ] to play the game.

3. Tap or click the price or Get button. If you see the Open button instead of a price or Get button, you already bought or downloaded that app.*

In the App Store, if an app has a Get button instead of a price, the app is free. You won't be charged for downloading a free app. Some free apps offer in-app purchases and subscriptions that you can buy. Subscriptions and in-app purchases give you access to more features, content, and more.