Bard, one of the many generative AI models available on the web, produced this short explanation:
Generative AI (GenAI) is a type of artificial intelligence that can create new content based on existing data. GenAI models learn patterns from the data they are trained on and then use this knowledge to generate new data with similar characteristics.
GenAI can create a wide variety of data, including: text, images, videos, audio, 3D models, computer code, and mathematical calculations and proofs.
This is a good start to understanding what all those AI apps are doing. It's more pattern recognition and prediction and less magic than it seems at first.
AI detection is very much an arms race right now. Things are changing so fast with both chatbots and detectors that the accuracy of these varies daily and sometimes from hour to hour. The best thing I can recommend if you encounter student work that you think has made unauthorized use of AI is to try several detectors and then discuss with the student to see if they know the material well. If you are willing to let them redo, making that clear early in the discussion may lead to a more fruitful conversation.