Human-computer interaction (HCI) is the field concerned with understanding, designing, and evaluating how people interact with computers and other interactive technologies. It focuses on both the technology and the people who use it.
HCI is interdisciplinary. It combines:
A system is useful if it provides functionality that helps a person accomplish their goal. A system is usable if people can accomplish that goal effectively, efficiently, and with relatively little difficulty.
Example: A calculator app can be extremely usable: the buttons are easy to understand, calculations happen quickly, and users can operate it without much difficulty. However, if a person is trying to edit a photograph, the calculator is not useful for that particular task.
Example: Metrash
A user may be trying to find and complete a government service on Metrash. The large number of categories and options can make it difficult to find the correct service. The design decision causing difficulty is organizing services into many categories that users may not know to look under.
Improvement: Add a prominent search bar so users can search directly for the service they need.
A prototype is an early version of a design that can be tested with users. Testing it helps designers identify problems, find ways to improve the design, and understand how users actually interact with it.
Example: Voice Input
Voice assistants are an example of interaction beyond a keyboard and mouse. They can benefit people with visual or physical disabilities because they allow users to interact without typing or using a mouse. To test whether voice input helps, I would compare users completing the same tasks with and without voice input and measure how quickly and successfully they complete them.
https://www.hcii.cmu.edu/about