User-centred design is a core approach of interaction design, meaning that every good interactive product is designed around the users, their environment and their activities, so that it is fit for purpose.

In order to support user-centred design, the interaction design process includes some fundamental activities.

You tried to use a device like your phone or remote control with heavy gloves or thick socks on your hands, which gave you an idea of how users with certain physical characteristics and in certain contexts might struggle, what their needs might be, and what changes you might have to make to meet those needs.
You then came up with alternative design ideas.
You drew up the alternative designs.
You tried ‘interacting’ with the drawings while wearing your gloves or socks, to see which might work better if it were to be developed into a product.

In other words, you conducted the four fundamental activities that make up the interaction design process – establishing requirements, designing alternatives, prototyping designs, and evaluating prototypes.

Establishing requirements – a requirement is a need that a particular interactive product must be able to satisfy. Establishing what is required of the product is essential to ensure that the interaction is the best possible fit for the user, both in terms of what the user needs to do with the product and how they experience the interaction. Requirements will depend on the characteristics of the user, the activities the user will perform using the product, and the environment in which the user interacts with the product. In the example of a phone or remote control, requirements are shaped by the need to use the device (e.g. mobile phone) to do certain activities (to make phone calls), given the size and mobility of the user’s hands (bigger than standard or fingerless) and the user’s physical environment (ski slope).
Designing alternatives – coming up with alternative designs enables designers to explore different ways of interpreting and satisfying the requirements for a particular interactive product. This is an essential and highly creative part of the process. In the phone and remote control example, this activity began when you started jotting down alternatives for the controls. Design ideas should be informed by fundamental design principles that derive from what we know about how our minds and bodies work.
Prototyping designs – once interaction designers have identified a number of possible ideas, they need to figure out which ones have the potential to work best for the users, their activities and their environment. To do this, designers need to prototype the most promising design ideas to make a first, often rough, model so that they can try them out. In the example of the phone or remote control, as you thought of different designs, you were also prototyping them by drawing the alternative interfaces you thought of. Prototyping can also be used to explore different aspects of a design.
Evaluating prototypes – evaluation enables designers to assess the limitations of a particular design, to find out to what extent a prototype meets requirements that have already been identified, to identify requirements that have not already emerged, and to establish what changes need to be made so that requirements are met.

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