Once an instance of a Constructor is created there are a number of methods in the prototype object of that constructor that can then be used to interact with that instance of the constructor.
A constructor or class is not always the best option. It does have some good points when it comes to anything where there might be more than one instance of something. However it might not be the best choice when it is just a single object, and there are other ways of handling things of course.
Constructors can be thought of as a situation in which there is one or more instances of an object that can be though of as a state, and then there are a number of methods that can be used to mutate that state. An alternative to this is to have a collection of pure functions that accept this state as an one of its arguments.