Declaratively
This tutorial will walk you through the common task of populating RadListBox with RadListBoxItems declaratively.
Here is a regular RadListBox declaration without items:
Declaring RadListBox
<telerik:RadListBox Width="200">
</telerik:RadListBox>
In order to add listbox items you need to use the RadListBox's Items property. The Items property is an ItemCollection which contains your RadListBoxItems. For example, insert the following lines to the declaration of your RadListBox and see how it will change.
Populating RadListBox with items
<telerik:RadListBox Width="200">
<telerik:RadListBoxItem Content="Australia" />
<telerik:RadListBoxItem Content="Brazil" />
<telerik:RadListBoxItem Content="Canada" />
<telerik:RadListBoxItem Content="China" />
<telerik:RadListBoxItem Content="England" />
<telerik:RadListBoxItem Content="Germany" />
</telerik:RadListBox>