Computer is like a kitchen in a hotel, and the Central Processing Unit is like a chef in that kitchen.
As a chef prepares food, the Central Processing Unit processes data in the computer and converts them into information.
As the food preparation speed depends on the speed of the chef, the speed of the computer depends on the speed of the Central Processing Unit.
A dual-core processor is like having a kitchen with two chefs preparing two meals, so two things can be prepared at the same time.