One of the key decisions in systems engineering is often where the boundary of a system - a collection of different parts working together to achieve some useful purpose - is defined. If a computer, as a system, is considered to consist only of its electronic components and doesn't include the user, it may be technically excellent...but still basically useless.
This is the situation that the art and science of human-computer interaction is supposed to avoid. When it comes to software, the most successful product isn't always the one with the best performance or the richest feature set: the offering with the most powerful and intuitive user interface often wins out.
A great deal of this kind of work is not just about the design of software interfaces and hardware interface devices (both input and output), but in studying user behavior, preferences, and experiences. The field is also no longer limited to helping to design computer applications: mobile, web, and VR interfaces offer additional challenges and opportunities to the human-computer interaction expert.
Human-computer interaction is rarely offered as a bachelor's degree. Instead, it is usually taken as a master's on top of undergraduate study in computer science, psychology, design, or some other relevant degree. This is the case at several universities in the United Kingdom, Switzerland, and the Netherlands, where a number of universities allow you to earn an advanced degree using English.