IoT app development for iOS and Android platforms leverages various technologies and tools to create connected applications. These apps connect to IoT devices, gather and process data, and allow users to control and monitor these devices. The development process involves using tools like Android Studio for Android and Xcode for iOS, and platforms like Google Cloud IoT Core and Firebase for managing data and building apps. Both platforms offer unique advantages, with Android using Java or Kotlin and iOS using Swift or Objective-C.