AppStore is missing after updating to iOS 10
Make sure you don't have Restrictions set up: go to Settings -> General -> Restrictions and make sure restrictions for deleting and downloading apps are off. Then find the App Store app:

On your home screen: Just tap its distinctive blue icon.

Using Siri:
Hold down your iPhone's home button and say, "Launch App Store".

Using Spotlight Search:
From your home screen, swipe your finger down from the center of the screen, then start typing "App Store".