How do I create my own Freezable class?

I've tried MSDN but there is not an example for deriving from Freezable.

Update:

Yes in the MSDN there's an example with animations but it's too complicated. need something simpler to understand freezable.

Documentation

In the MSDN documentation of the Freezable class, in the Remarks section, you can find the following paragraph:

For information on using and creating your own Freezable objects, see Freezable Objects Overview.

This overview contains a section Creating Your Own Freezable Class, which contains the theoretical background for what you want to do. To find an example, follow the link at the bottom of that section:

For an example of a custom Freezable class, see the Custom Animation Sample.

---

Example

Since you specifically asked for a simple example, here is one (adapted from the MSDN page of Freezable.CreateInstanceCore). Remember the following sentence from the theory page:

Every Freezable subclass must override the CreateInstanceCore method. If your class uses dependency properties for all its data, you're finished.

Let's say we make a custom class MySimpleColor, which has exactly one boolean property IsRed. To make this class Freezable, we just have to override CreateInstanceCore:

public class MySimpleColor : Freezable
{
    // Here are your properties
    public static readonly DependencyProperty IsRedProperty = 
        DependencyProperty.Register("IsRed", typeof(Boolean), typeof(MySimpleColor));

    // CLR accessor of your property
    public bool IsRed {
        get { return (bool)GetValue(IsRedProperty); }
        set { SetValue(IsRedProperty, value); }
    }

    // All that's needed to make this Freezable
    protected override Freezable CreateInstanceCore() {
        return new MySimpleColor();      
    }
}

That's it. The code inherited from Freezable ensures that the Freezable methods such as Freeze() or Clone() work exactly as intended.