If what you really need is an explaination of the concepts of classes as the title suggests, maybe this will help:

Think of objects in coding just as you would objects in the real world.

A Dodge Ram is an object.
It is made up of smaller objects: Engine, doors, tires
Each of those is made up of smaller objects: Bolts, pistons, etc.

Objects in coding can inherit from each other, usually from the general to the specific.

• Class vehicle
  
  • Class truck : vehicle
    
    • Class Ram : Truck
      
      • class 2500FWD : Ram

A class is the blueprint for instanciating (making an instance of) the object.

DodgeRam is a class describing how to make an instance, but itself is not an actual thing you can interact with.

myDodgeRam is an instance of a the class DodgeRam

I can do things with the object instance myDodgeRam

myDodgeRam.SerialNumber = 123456789;
myDodgeRam.FillUpTank();
float fuelLevel = myDodgeRam.FuelTankPercentageFull;
if (myDodgeRam.IsReady) myDodgeRam.StartEngine();

Anything defined in the base class is available to a child.

class truck : vehicle
{

    public float FuelTankPercentageFull
    {
       get; set;
    }
}

class DodgeRam : truck
{
    // I don't have to define a FuelTankPercentageFull here because I inherit it from my parent
}

Methods defined as virtual in the base class can be overridden by the child class (at least in .NET languages like C#). This is often to account for more specific needs.

class truck : vehicle
{

    public virtual bool StartEngine()
    {
       // Do something to start the engine
       return true; // No checks or requirements
    }
}

class DodgeRam : truck
{
    public override bool StartEngine()
    {
        // Do a safety check first
        if (IsSeatBeltsEngaged && IsFootOnBrake)
        { 
            return true;
        }
        return false;
    }
}

You can even have a child class call the base classes methods which is often the smart way to go.

class truck : vehicle
{

    public virtual bool StartEngine()
    {
       // Notice there are no safety checks before trying to start up.
       try
       {
          // Do something to start the engine
          return true; // because we succeeded
       }
       catch(exception error)
       {
           return false; // because there was an error
       }
    }
}

class DodgeRam : truck
{
    public override bool StartEngine()
    {
        // Do a safety check first
        if (IsSeatBeltsEngaged && IsFootOnBrake)
        { 
            return base.StartEngine();
            // Now all the electrical work is in the base class
            // and not repeated in every child.
        }
    }
}