What is it
Design systems are a set of design patterns that ensure consistency of brand and functionality.
The challenge of keeping brand aligned and consistent grows with the amount of user interfaces an organization is exposing. There is also a large cost of reinveting the wheel by designing and building new basic components in each new project and still make them accessible, beautiful, functional and up-to-date with the latest brand. The article And You Thought Buttons Were Easy shows a fantastic example of how expensive making buttons can be in a large organization if they are not reused throughout projects.
By using design systems, less time, energy and money can be spent on reinventing common user interface components—energy that is better used on strategic work of making the products better.
When to use it
Always lean on design systems when building user interfaces.
Einride UI is a design system with visual components that adhere to Einride's brand. Use it for as many components as possible. If you have a need of using complex components that are not yet implemented in Einride UI, MUI can be used.
How to learn it
Audrey Hacq has written a thorough article titled Everything you need to know about Design Systems which is a really good introduction to the concept of design systems. Another good way of learning about design systems is to look at some examples. Two such examples are Google's Material Design and Atlassian's Design System.