Computer aided design (CAD) was primarily designed for designers, architects, and engineers to be used for 2D and 3D modeling. From hereon, I will refer to users of CAD tools as designers.
Designers use CAD tools for many reasons. After the designer has an initial idea or sketch in their mind, they can use such tools to create a model. This model can then be used to manufacture the design via 3D printing or more traditional approaches. This process requires multiple iterations to ensure the design is correct and simple to manufacture. CAD allows an idea to become a reality.
CAD tools were primarily created to avoid large manufacturing costs. Without such tools, a designer would need to send their work to a manufacturer, which would cost a large sum of money, and then they would have to wait for the design to return. However, after it is returned, there would be no guarantee the design would work as designed. With CAD, the designers can verify their work and thus have a high rate of success when actually being manufactured.
Primarily used by Engineers
Engineers may use CAD tools for Printed Circuit Board (PCB) and circuit design. The turn-around costs for producing a PCB is extremely high and requires time. Therefore, by verifying the circuity on a CAD tool, the engineer has a lower cost and has increased guarantee their design is accurate.
Primarily used by Architects
Did you know that the home you live in may have potentially been designed in a CAD tool? Architects are using CAD tools for designing buildings and household. Due to the large manufacturing costs of large infrastructures, CAD tools provides a method of verification. In addition to developing houses and buildings, architects can also use such tools for designing buildings, roads, and other critical infrastructure. Interestingly, CAD tools allow architects (and in some cases civil engineers) to do stress testing. This includes testing to check if the infrastructure can handle natural events, e.g. storms.
In conclusion, computer aided design is used primarily by designers to create 2D and 3D models. Even items such as a fork, spoon, and bigger items like your laptop were designed via CAD software. Knowledge of such tools is essential if one wants to design products for consumers. However, learning CAD does not require a traditional university degree and thus anyone can learn it by practicing. We encourage you to look around the website for CAD exercises, which can teach you how to design.