Suppose we have a class Called Student. If we want to access any of it's member functions or data members, we first have to create it's instance to access them as they are non-static.
In SpringBoot, we are more concerned about the business login than creating instances, so we leave it on SpringBoot to handle. In SpringBoot we have a concept of Container where we store all the objects and access them whenever needed.
We can access them by creating a ApplicationContext context. But in order to let SpringBoot to create a class's instance, we need to tell Spring that we need a particular class instance by simply using the @Component annotation. Instances of classes created are referred to as Bean in SpringBoot and we access them by using the getBean() method.
If one of your class is dependent on the other class's instance, then we use the @Autowired annotation to let SpringBoot handle the instances as we cannot directly handle them from the context.