Unfortunately I should confirm that our documentation only mentions the control but lacks of detailed information on it. I logged a feedback item and sent it to our documentation team for them to improve the help article. Also please mind that the control was renamed and split in two -- RadHorizontalDataAxis and RadVerticalDataAxis. As their name implies they are specially made to be used in different layouts - horizontal and vertical.
Please take a look at our DataBar control's Theming demo in the QSF to see the Axis in action and with sample code provided.
Telerik by Progress
Want to extend the target reach of your WPF applications, leveraging iOS, Android, and UWP? Try UI for Xamarin
, a suite of polished and feature-rich components for the Xamarin framework, which allow you to write beautiful native mobile apps using a single shared C# codebase.