When developing for iOS devices (iPad, iPad Pro, iPad Mini, iPhone, iPod Touch) you need to have Xcode installed on your computer. Xcode is also required for developing for macOS devices.

Using the Build Settings interface, you can identify your version of Xcode and decide whether you want to run it as a release or in debug mode. You can decide whether you want your Xcode project to directly reference the Unity iOS runtime library from the Unity Editor's install location. This is accomplished by selecting the Symlink Unity libraries checkbox. You should not use this for your final build:

You will also decide whether this is a development build or not. If it is, you will have the additional options of Autoconnect Profiler, Script Debugging, and Scripts Only Build.