Android NDK (C)
Unity (AR Foundation)
The user's device has cameras (usually both front and back) and various sensors, such as an accelerometer, that provide data to your AR app for interpreting the real world. The camera itself may have a depth sensor and be able to determine the range, dimensions, and other useful data about the targets it detects.
For your AR app, you configure the camera for optimal performance. You can also use camera image metadata, frame buffering, and shared camera access to tune performance. The guides above describe some of the AR camera capabilities for each platform.