In JavaScript, object-oriented programming (OOP) is a programming paradigm centered around the concept of classes, which serve as blueprints for creating objects.

Classes are used to define the structure and behavior of the objects created from them called instances, specifying fields (properties) to hold data and methods (functions) to operate on that data.

Overall, they allow developers to create reusable, modular code that models real-world entities (e.g., a user, an animal, etc) and their relationships.

Declaring a new class

To declare a new class, you can use the class keyword as follows:

class ClassName {  // class body}

Where ClassName is the user-defined name of the class.

Note: By convention, class names always start with a capital letter.

Instantiating a class

To create an instance of a class (an object), you can use the new keyword, followed by the name of the class, and a pair of parentheses ():

let object = new ClassName();

Class fields

A class field is a property defined within a class, that allows you to define and initialize properties for objects created from that class.