WPF Data Binding TooWay XAML to C# and C# to XAML

I have XAML code:

<TextBox Name="textBoxMask1"/>
<TextBox Name="textBoxMask2"/>
<TextBox Name="textBoxMask3"/>
...
<TextBox Name="textBoxMask9"/>

and class in C#:

private static string mask1;
public static string Mask1
{
    get { return mask1; }
    set { mask1 = value; }
}

private static string mask2;
public static string Mask2
{
    get { return mask2; }
    set { mask2 = value; }
}

private static string mask3;
public static string Mask3
{
    get { return mask3; }
    set { mask3 = value; }
}
....
private static string mask9;
public static string Mask9
{
    get { return mask9; }
    set { mask9 = value; }
}

And I want to bind these TextBoxes with Properties -> textBoxMask1 with Mask1 etc. Earlier I did this by TextChanged, but I want to make Binding. TooWay Binding, because I want to predefine Mask1, Mask2, Mask3, ..., Mask9 in another C# class, and maybe later change these values - also in some C# code - and I want my changes, to be visible in layout (XAML) and in C# code - so ex. changing Property Mask1 from C# will change Text in TextBox textBoxMask1, and changing Text in textBoxMask1 will change Property Mask1. I don't understand, how to make connection (binding) between objects XAML and C#.

Copyright Notice：Content Author:「Namek」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/14043483/wpf-data-binding-tooway-xaml-to-c-sharp-and-c-sharp-to-xaml