1- What is HCI and which disciplines contribute to it? Human-computer interaction (HCI) is the study of how people interact with computers. The goal isn't simply to make tech work, but to make it understandable and appropriate for the people using it. HCI is inherently interdisciplinary. It mixes design, psychology, and cognitive sciences, and we also need to understand the users's goals and expectations. There is many rules and heurstics one could follow, but here is a simple one

2- Useful vs. usable something is useful when it does a goal we have, and it is usable when we can use it to finish the job efficiently and with minimal effort. Imagine a fitness app with great UX. it would be both useful and usable for an athlete, but it'd not be useful for a normal person who is not interested in fitness. for more on accessibility and usefullness, read the following W3C article

3- an example of a confusing design and how to improve it: A microwave with too many buttons. I just want to heat my food man. I do not want to struggle my way between the buttons at 3am. A better design should have a quick set up button that just heats up the food normally without considering all those fancy options

4- what is a prototype, and how can testing it with users help? a prototype is an early representation of a product or app. it allows designers to test ideas before spending the time implementing them. Asking "do you like it" is not a good idea because one might like the visual identitiy of an app, but can't locate an important feature they want in it. it is important in the testing to follow the UX principles` found in this video

5- Example of interaction beyond keyboard and mouse a device you put in a cup and it beeps when the liquid reaches near the top. it helps blind people, and we can test it by seeing the spillage rate over multiple testers.