Engineers invent many products. These products can range from machinery to ventilation systems to cars. Engineers that invent such products are mechanical engineers because they work with a mechanized principle. When a team of people have an idea, they brainstorm concepts of the idea, and turn it into a physical entity by means of manufacturing and production.
Computer engineers specialize in inventing new computers and phones. Without them, you will have no iPhones and fast-running laptops.
Electrical engineers specialize in inventing new telecommunications, such as intercom, computer chips, and other circuitry components.