A class is a blueprint. An object is a thing built from that blueprint. Think of a class as a cookie cutter and objects as the cookies.
The class Dog describes what every dog has: a name, a breed, and a method called bark(). But the class itself is not a dog. When you create an object from Dog, you get a specific dog with a specific name and breed.
You can create as many objects as you want from one class. Each object is independent. Changing one dog's name does not affect any other dog. The class defines the structure. The objects hold the actual data.