OOPS - What Is a Class?

Simply a class is a blue print from which individual objects are created.

In the real world, you'll often find many individual objects all of the same kind. There may be thousands of other bicycles in existence, all of the same make and model. Each bicycle was built from the same set of blueprints and therefore contains the same components. In object-oriented terms, we say that your bicycle is an instance of the class of objects known as bicycles. A class is the blueprint from which individual objects are created.

Its better if you can refer to an example right, take a look

class Bicycle {
    int cadence = 0;
    int speed = 0;
    int gear = 1;
    void changeCadence(int newValue) {
         cadence = newValue;
    }
    void changeGear(int newValue) {
         gear = newValue;
    }
    void speedUp(int increment) {
         speed = speed + increment;  
    }
    void applyBrakes(int decrement) {
         speed = speed - decrement;
    }
    void printStates() {
         System.out.println("cadence:" +
             cadence + " speed:" +
             speed + " gear:" + gear);
    }
}

The fields cadence, speed, and gear represent the object's state, and the methods (changeCadence, changeGear, speedUp etc.) define its interaction with the outside world.

A class can contain any of the following variable types.

Local variables . variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed.

Instance variables . Instance variables are variables within a class but outside any method. These variables are instantiated when the class is loaded. Instance variables can be accessed from inside any method, constructor or blocks of that particular class.

Class variables . Class variables are variables declared with in a class, outside any method, with the static keyword.

Now take a look at how we can create an instance of this class ie an Object

class BicycleDemo {

    public static void main(String[] args) {
        // Create two different Bicycle objects
        Bicycle bike1 = new Bicycle();
        Bicycle bike2 = new Bicycle();
        // Invoke methods on those objects
        bike1.changeCadence(50);
        bike1.speedUp(10);  
     }
  
   }

Now you have an idea of  'what is a class', 'how to create a class', 'how to create instance of a class'...
Long way to go...be confident with basics....Now its time to focus on basics...