OneWay   source --> target
TwoWay    source <-> target
OneTime    source -> target only once
OneWayToSource  source <- target
Default  is OneWay   (except for textboxes(it is Twoway for textbox)

Simple element binding
<Slider Name="mySlider"
        Margin="3"
        Minimum="1"
        Maximum="40"
        Value="10"
        TickFrequency="1"
        TickPlacement="TopLeft">
</Slider>

<TextBlock Margin="81,126,185,125"
            Text="Simple Text"
            Name="myTextBox"
            FontSize="{Binding ElementName=mySlider, Path=Value, Mode=TwoWay}">
</TextBlock>

 

To do samething programmatically

Binding b = new Binding();
b.Source = mySlider;
b.Path = new PropertyPath("Value");
b.Mode = BindingMode.TwoWay;

//BindingOperations.ClearAllBindings(myTextBox); // a way to reset
myTextBox.SetBinding(TextBlock.FontSizeProperty, b);

If you are not binding to an element, you are binding to one of the following
(instead of ElementName=)
Source. object that's supplying .
RelativeSource. path or pointer to source object.
DataContext. finding by nearest parents datacontext object

Calling system resource/ window resource
    <Window.Resources>
        <FontFamily x:Key="windowResource">sometext</FontFamily>
    </Window.Resources>

<TextBlock Text="{Binding Source={x:Static SystemFonts.IconFontFamily}, Path=Source}"></TextBlock>
<TextBlock Text="{Binding Source={StaticResource windowResource},Path=Source}"></TextBlock>